Mirror changes from mono/coreclr (#16713)

* Remove stale SuppressMessage attributes (dotnet/coreclr#26501)

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>

* Use null coalescing assignment operator in more places

There's currently no auto-fix for this, so the fixes were done manually.

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>

* Fix IDE0026 (use expression-bodied members for indexers)

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>

63 files changed, 280 insertions, 716 deletions

diff --git a/netcore/System.Private.CoreLib/shared/System/AggregateException.cs b/netcore/System.Private.CoreLib/shared/System/AggregateException.cs
index e24ad1939b0..3486a4fdbf0 100644
--- a/netcore/System.Private.CoreLib/shared/System/AggregateException.cs
+++ b/netcore/System.Private.CoreLib/shared/System/AggregateException.cs
@@ -339,11 +339,7 @@ namespace System
                 // exceptions (to be rethrown later) and add it.
                 if (!predicate(m_innerExceptions[i]))
                 {
-                    if (unhandledExceptions == null)
-                    {
-                        unhandledExceptions = new List<Exception>();
-                    }
-
+                    unhandledExceptions ??= new List<Exception>();
                     unhandledExceptions.Add(m_innerExceptions[i]);
                 }
             }
diff --git a/netcore/System.Private.CoreLib/shared/System/Array.cs b/netcore/System.Private.CoreLib/shared/System/Array.cs
index d2b9aca96b4..606cf8973d4 100644
--- a/netcore/System.Private.CoreLib/shared/System/Array.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Array.cs
@@ -477,7 +477,7 @@ namespace System
             if (array.Rank != 1)
                 ThrowHelper.ThrowRankException(ExceptionResource.Rank_MultiDimNotSupported);
 
-            if (comparer == null) comparer = Comparer.Default;
+            comparer ??= Comparer.Default;
 #if CORECLR
             if (comparer == Comparer.Default)
             {
diff --git a/netcore/System.Private.CoreLib/shared/System/BadImageFormatException.cs b/netcore/System.Private.CoreLib/shared/System/BadImageFormatException.cs
index f9072e98098..e3edaebb0bd 100644
--- a/netcore/System.Private.CoreLib/shared/System/BadImageFormatException.cs
+++ b/netcore/System.Private.CoreLib/shared/System/BadImageFormatException.cs
@@ -107,8 +107,7 @@ namespace System
 
             if (_fusionLog != null)
             {
-                if (s == null)
-                    s = " ";
+                s ??= " ";
                 s += Environment.NewLine;
                 s += Environment.NewLine;
                 s += _fusionLog;
diff --git a/netcore/System.Private.CoreLib/shared/System/Collections/ArrayList.cs b/netcore/System.Private.CoreLib/shared/System/Collections/ArrayList.cs
index 53c7d79dc33..7607145e3a4 100644
--- a/netcore/System.Private.CoreLib/shared/System/Collections/ArrayList.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Collections/ArrayList.cs
@@ -811,8 +811,7 @@ namespace System.Collections
                 if (Count - index < count)
                     throw new ArgumentException(SR.Argument_InvalidOffLen);
 
-                if (comparer == null)
-                    comparer = Comparer.Default;
+                comparer ??= Comparer.Default;
 
                 int lo = index;
                 int hi = index + count - 1;
@@ -904,7 +903,6 @@ namespace System.Collections
                 return _list.IndexOf(value);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int IndexOf(object? value, int startIndex)
             {
                 return IndexOf(value, startIndex, _list.Count - startIndex);
@@ -970,13 +968,11 @@ namespace System.Collections
                 return LastIndexOf(value, _list.Count - 1, _list.Count);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex)
             {
                 return LastIndexOf(value, startIndex, startIndex + 1);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex, int count)
             {
                 if (_list.Count == 0)
@@ -1216,7 +1212,6 @@ namespace System.Collections
                         return _list.Capacity;
                     }
                 }
-                [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
                 set
                 {
                     lock (_root)
@@ -1290,7 +1285,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int BinarySearch(int index, int count, object? value, IComparer? comparer)
             {
                 lock (_root)
@@ -1339,7 +1333,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void CopyTo(int index, Array array, int arrayIndex, int count)
             {
                 lock (_root)
@@ -1356,7 +1349,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override IEnumerator GetEnumerator(int index, int count)
             {
                 lock (_root)
@@ -1373,7 +1365,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int IndexOf(object? value, int startIndex)
             {
                 lock (_root)
@@ -1382,7 +1373,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int IndexOf(object? value, int startIndex, int count)
             {
                 lock (_root)
@@ -1399,7 +1389,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void InsertRange(int index, ICollection c)
             {
                 lock (_root)
@@ -1416,7 +1405,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex)
             {
                 lock (_root)
@@ -1425,7 +1413,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex, int count)
             {
                 lock (_root)
@@ -1450,7 +1437,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void RemoveRange(int index, int count)
             {
                 lock (_root)
@@ -1459,7 +1445,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void Reverse(int index, int count)
             {
                 lock (_root)
@@ -1468,7 +1453,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void SetRange(int index, ICollection c)
             {
                 lock (_root)
@@ -1477,7 +1461,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override ArrayList GetRange(int index, int count)
             {
                 lock (_root)
@@ -1502,7 +1485,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void Sort(int index, int count, IComparer? comparer)
             {
                 lock (_root)
@@ -1519,7 +1501,6 @@ namespace System.Collections
                 }
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override Array ToArray(Type type)
             {
                 lock (_root)
@@ -1766,7 +1747,6 @@ namespace System.Collections
                 throw new NotSupportedException(SR.NotSupported_FixedSizeCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int BinarySearch(int index, int count, object? value, IComparer? comparer)
             {
                 return _list.BinarySearch(index, count, value, comparer);
@@ -1775,7 +1755,6 @@ namespace System.Collections
             public override int Capacity
             {
                 get => _list.Capacity;
-                [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
                 set => throw new NotSupportedException(SR.NotSupported_FixedSizeCollection);
             }
 
@@ -1801,7 +1780,6 @@ namespace System.Collections
                 _list.CopyTo(array, index);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void CopyTo(int index, Array array, int arrayIndex, int count)
             {
                 _list.CopyTo(index, array, arrayIndex, count);
@@ -1812,7 +1790,6 @@ namespace System.Collections
                 return _list.GetEnumerator();
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override IEnumerator GetEnumerator(int index, int count)
             {
                 return _list.GetEnumerator(index, count);
@@ -1823,13 +1800,11 @@ namespace System.Collections
                 return _list.IndexOf(value);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int IndexOf(object? value, int startIndex)
             {
                 return _list.IndexOf(value, startIndex);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int IndexOf(object? value, int startIndex, int count)
             {
                 return _list.IndexOf(value, startIndex, count);
@@ -1840,7 +1815,6 @@ namespace System.Collections
                 throw new NotSupportedException(SR.NotSupported_FixedSizeCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void InsertRange(int index, ICollection c)
             {
                 throw new NotSupportedException(SR.NotSupported_FixedSizeCollection);
@@ -1851,13 +1825,11 @@ namespace System.Collections
                 return _list.LastIndexOf(value);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex)
             {
                 return _list.LastIndexOf(value, startIndex);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex, int count)
             {
                 return _list.LastIndexOf(value, startIndex, count);
@@ -1873,13 +1845,11 @@ namespace System.Collections
                 throw new NotSupportedException(SR.NotSupported_FixedSizeCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void RemoveRange(int index, int count)
             {
                 throw new NotSupportedException(SR.NotSupported_FixedSizeCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void SetRange(int index, ICollection c)
             {
                 _list.SetRange(index, c);
@@ -1896,14 +1866,12 @@ namespace System.Collections
                 return new Range(this, index, count);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void Reverse(int index, int count)
             {
                 _list.Reverse(index, count);
                 _version = _list._version;
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void Sort(int index, int count, IComparer? comparer)
             {
                 _list.Sort(index, count, comparer);
@@ -1915,7 +1883,6 @@ namespace System.Collections
                 return _list.ToArray();
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override Array ToArray(Type type)
             {
                 return _list.ToArray(type);
@@ -2033,7 +2000,6 @@ namespace System.Collections
                 throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int BinarySearch(int index, int count, object? value, IComparer? comparer)
             {
                 return _list.BinarySearch(index, count, value, comparer);
@@ -2043,7 +2009,6 @@ namespace System.Collections
             public override int Capacity
             {
                 get => _list.Capacity;
-                [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
                 set => throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
             }
 
@@ -2069,7 +2034,6 @@ namespace System.Collections
                 _list.CopyTo(array, index);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void CopyTo(int index, Array array, int arrayIndex, int count)
             {
                 _list.CopyTo(index, array, arrayIndex, count);
@@ -2080,7 +2044,6 @@ namespace System.Collections
                 return _list.GetEnumerator();
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override IEnumerator GetEnumerator(int index, int count)
             {
                 return _list.GetEnumerator(index, count);
@@ -2091,13 +2054,11 @@ namespace System.Collections
                 return _list.IndexOf(value);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int IndexOf(object? value, int startIndex)
             {
                 return _list.IndexOf(value, startIndex);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int IndexOf(object? value, int startIndex, int count)
             {
                 return _list.IndexOf(value, startIndex, count);
@@ -2108,7 +2069,6 @@ namespace System.Collections
                 throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void InsertRange(int index, ICollection c)
             {
                 throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
@@ -2119,13 +2079,11 @@ namespace System.Collections
                 return _list.LastIndexOf(value);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex)
             {
                 return _list.LastIndexOf(value, startIndex);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex, int count)
             {
                 return _list.LastIndexOf(value, startIndex, count);
@@ -2141,13 +2099,11 @@ namespace System.Collections
                 throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void RemoveRange(int index, int count)
             {
                 throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void SetRange(int index, ICollection c)
             {
                 throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
@@ -2163,13 +2119,11 @@ namespace System.Collections
                 return new Range(this, index, count);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void Reverse(int index, int count)
             {
                 throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void Sort(int index, int count, IComparer? comparer)
             {
                 throw new NotSupportedException(SR.NotSupported_ReadOnlyCollection);
@@ -2180,7 +2134,6 @@ namespace System.Collections
                 return _list.ToArray();
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override Array ToArray(Type type)
             {
                 return _list.ToArray(type);
@@ -2521,13 +2474,11 @@ namespace System.Collections
                 return -1;
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex)
             {
                 return LastIndexOf(value, startIndex, startIndex + 1);
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int LastIndexOf(object? value, int startIndex, int count)
             {
                 InternalUpdateRange();
@@ -2586,7 +2537,6 @@ namespace System.Collections
                 InternalUpdateVersion();
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override void SetRange(int index, ICollection c)
             {
                 InternalUpdateRange();
diff --git a/netcore/System.Private.CoreLib/shared/System/Collections/Generic/ArraySortHelper.cs b/netcore/System.Private.CoreLib/shared/System/Collections/Generic/ArraySortHelper.cs
index 4234a3ac5f2..888b97688cc 100644
--- a/netcore/System.Private.CoreLib/shared/System/Collections/Generic/ArraySortHelper.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Collections/Generic/ArraySortHelper.cs
@@ -58,11 +58,7 @@ namespace System.Collections.Generic
             // underlying IComparables, etc) that are bogus.
             try
             {
-                if (comparer == null)
-                {
-                    comparer = Comparer<T>.Default;
-                }
-
+                comparer ??= Comparer<T>.Default;
                 IntrospectiveSort(keys, index, length, comparer.Compare);
             }
             catch (IndexOutOfRangeException)
@@ -79,11 +75,7 @@ namespace System.Collections.Generic
         {
             try
             {
-                if (comparer == null)
-                {
-                    comparer = Comparer<T>.Default;
-                }
-
+                comparer ??= Comparer<T>.Default;
                 return InternalBinarySearch(array, index, length, value, comparer);
             }
             catch (Exception e)
diff --git a/netcore/System.Private.CoreLib/shared/System/Collections/Generic/Dictionary.cs b/netcore/System.Private.CoreLib/shared/System/Collections/Generic/Dictionary.cs
index 7253577c097..8a19f04318c 100644
--- a/netcore/System.Private.CoreLib/shared/System/Collections/Generic/Dictionary.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Collections/Generic/Dictionary.cs
@@ -152,59 +152,17 @@ namespace System.Collections.Generic
 
         public int Count => _count - _freeCount;
 
-        public KeyCollection Keys
-        {
-            get
-            {
-                if (_keys == null) _keys = new KeyCollection(this);
-                return _keys;
-            }
-        }
+        public KeyCollection Keys => _keys ??= new KeyCollection(this);
 
-        ICollection<TKey> IDictionary<TKey, TValue>.Keys
-        {
-            get
-            {
-                if (_keys == null) _keys = new KeyCollection(this);
-                return _keys;
-            }
-        }
+        ICollection<TKey> IDictionary<TKey, TValue>.Keys => _keys ??= new KeyCollection(this);
 
-        IEnumerable<TKey> IReadOnlyDictionary<TKey, TValue>.Keys
-        {
-            get
-            {
-                if (_keys == null) _keys = new KeyCollection(this);
-                return _keys;
-            }
-        }
+        IEnumerable<TKey> IReadOnlyDictionary<TKey, TValue>.Keys => _keys ??= new KeyCollection(this);
 
-        public ValueCollection Values
-        {
-            get
-            {
-                if (_values == null) _values = new ValueCollection(this);
-                return _values;
-            }
-        }
+        public ValueCollection Values => _values ??= new ValueCollection(this);
 
-        ICollection<TValue> IDictionary<TKey, TValue>.Values
-        {
-            get
-            {
-                if (_values == null) _values = new ValueCollection(this);
-                return _values;
-            }
-        }
+        ICollection<TValue> IDictionary<TKey, TValue>.Values => _values ??= new ValueCollection(this);
 
-        IEnumerable<TValue> IReadOnlyDictionary<TKey, TValue>.Values
-        {
-            get
-            {
-                if (_values == null) _values = new ValueCollection(this);
-                return _values;
-            }
-        }
+        IEnumerable<TValue> IReadOnlyDictionary<TKey, TValue>.Values => _values ??= new ValueCollection(this);
 
         public TValue this[TKey key]
         {
diff --git a/netcore/System.Private.CoreLib/shared/System/Collections/Hashtable.cs b/netcore/System.Private.CoreLib/shared/System/Collections/Hashtable.cs
index 119d768fc86..6314f5f24dd 100644
--- a/netcore/System.Private.CoreLib/shared/System/Collections/Hashtable.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Collections/Hashtable.cs
@@ -830,15 +830,7 @@ namespace System.Collections
         // to the hash table are reflected in this collection.  It is not
         // a static copy of all the keys in the hash table.
         //
-        public virtual ICollection Keys
-        {
-            get
-            {
-                if (_keys == null)
-                    _keys = new KeyCollection(this);
-                return _keys;
-            }
-        }
+        public virtual ICollection Keys => _keys ??= new KeyCollection(this);
 
         // Returns a collection representing the values of this hashtable. The
         // order in which the returned collection represents the values is
@@ -850,15 +842,7 @@ namespace System.Collections
         // to the hash table are reflected in this collection.  It is not
         // a static copy of all the keys in the hash table.
         //
-        public virtual ICollection Values
-        {
-            get
-            {
-                if (_values == null)
-                    _values = new ValueCollection(this);
-                return _values;
-            }
-        }
+        public virtual ICollection Values => _values ??= new ValueCollection(this);
 
         // Inserts an entry into this hashtable. This method is called from the Set
         // and Add methods. If the add parameter is true and the given key already
diff --git a/netcore/System.Private.CoreLib/shared/System/Collections/ObjectModel/ReadOnlyCollection.cs b/netcore/System.Private.CoreLib/shared/System/Collections/ObjectModel/ReadOnlyCollection.cs
index 4791ae7dd80..59f92233267 100644
--- a/netcore/System.Private.CoreLib/shared/System/Collections/ObjectModel/ReadOnlyCollection.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Collections/ObjectModel/ReadOnlyCollection.cs
@@ -26,10 +26,7 @@ namespace System.Collections.ObjectModel
 
         public int Count => list.Count;
 
-        public T this[int index]
-        {
-            get { return list[index]; }
-        }
+        public T this[int index] => list[index];
 
         public bool Contains(T value)
         {
diff --git a/netcore/System.Private.CoreLib/shared/System/ComponentModel/DefaultValueAttribute.cs b/netcore/System.Private.CoreLib/shared/System/ComponentModel/DefaultValueAttribute.cs
index 428464c6c0b..66e8c758875 100644
--- a/netcore/System.Private.CoreLib/shared/System/ComponentModel/DefaultValueAttribute.cs
+++ b/netcore/System.Private.CoreLib/shared/System/ComponentModel/DefaultValueAttribute.cs
@@ -12,8 +12,6 @@ namespace System.ComponentModel
     /// <summary>
     /// Specifies the default value for a property.
     /// </summary>
-    [SuppressMessage("Microsoft.Design", "CA1019:DefineAccessorsForAttributeArguments")]
-    [SuppressMessage("Microsoft.Performance", "CA1813:AvoidUnsealedAttributes")]
     [AttributeUsage(AttributeTargets.All)]
     public class DefaultValueAttribute : Attribute
     {
diff --git a/netcore/System.Private.CoreLib/shared/System/CurrentSystemTimeZone.cs b/netcore/System.Private.CoreLib/shared/System/CurrentSystemTimeZone.cs
index 2df633396a6..01a94934829 100644
--- a/netcore/System.Private.CoreLib/shared/System/CurrentSystemTimeZone.cs
+++ b/netcore/System.Private.CoreLib/shared/System/CurrentSystemTimeZone.cs
@@ -136,14 +136,12 @@ namespace System
 
         private static DaylightTime CreateDaylightChanges(int year)
         {
-            DaylightTime? currentDaylightChanges = null;
+            DateTime start = DateTime.MinValue;
+            DateTime end = DateTime.MinValue;
+            TimeSpan delta = TimeSpan.Zero;
 
             if (TimeZoneInfo.Local.SupportsDaylightSavingTime)
             {
-                DateTime start;
-                DateTime end;
-                TimeSpan delta;
-
                 foreach (TimeZoneInfo.AdjustmentRule rule in TimeZoneInfo.Local.GetAdjustmentRules())
                 {
                     if (rule.DateStart.Year <= year && rule.DateEnd.Year >= year && rule.DaylightDelta != TimeSpan.Zero)
@@ -151,19 +149,12 @@ namespace System
                         start = TimeZoneInfo.TransitionTimeToDateTime(year, rule.DaylightTransitionStart);
                         end = TimeZoneInfo.TransitionTimeToDateTime(year, rule.DaylightTransitionEnd);
                         delta = rule.DaylightDelta;
-
-                        currentDaylightChanges = new DaylightTime(start, end, delta);
                         break;
                     }
                 }
             }
 
-            if (currentDaylightChanges == null)
-            {
-                currentDaylightChanges = new DaylightTime(DateTime.MinValue, DateTime.MinValue, TimeSpan.Zero);
-            }
-
-            return currentDaylightChanges;
+            return new DaylightTime(start, end, delta);
         }
 
         public override TimeSpan GetUtcOffset(DateTime time)
diff --git a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Contracts/Contracts.cs b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Contracts/Contracts.cs
index c424fc12c14..6b9707fdf10 100644
--- a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Contracts/Contracts.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Contracts/Contracts.cs
@@ -640,8 +640,7 @@ namespace System.Diagnostics.Contracts
                 }
             }
 
-            if (probablyNotRewritten == null)
-                probablyNotRewritten = thisAssembly;
+            probablyNotRewritten ??= thisAssembly;
             string? simpleName = probablyNotRewritten.GetName().Name;
             ContractHelper.TriggerFailure(kind, SR.Format(SR.MustUseCCRewrite, contractKind, simpleName), null, null, null);
         }
diff --git a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/ActivityTracker.cs b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/ActivityTracker.cs
index 0f476912885..00e080d05c2 100644
--- a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/ActivityTracker.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/ActivityTracker.cs
@@ -184,8 +184,7 @@ namespace System.Diagnostics.Tracing
                     if (orphan.CanBeOrphan())
                     {
                         // We can't pop anything after we see a valid orphan, remember this for later when we update m_current.
-                        if (newCurrentActivity == null)
-                            newCurrentActivity = orphan;
+                        newCurrentActivity ??= orphan;
                     }
                     else
                     {
@@ -201,8 +200,7 @@ namespace System.Diagnostics.Tracing
                     // I succeeded stopping this activity. Now we update our m_current pointer
 
                     // If I haven't yet determined the new current activity, it is my creator.
-                    if (newCurrentActivity == null)
-                        newCurrentActivity = activityToStop.m_creator;
+                    newCurrentActivity ??= activityToStop.m_creator;
 
                     m_current.Value = newCurrentActivity;
 
diff --git a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventProvider.cs b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventProvider.cs
index 6a3d373fe63..a805605fec5 100644
--- a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventProvider.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventProvider.cs
@@ -100,7 +100,6 @@ namespace System.Diagnostics.Tracing
         private const int s_etwAPIMaxRefObjCount = 8;
         private const int s_traceEventMaximumSize = 65482;
 
-        [SuppressMessage("Microsoft.Design", "CA1034:NestedTypesShouldNotBeVisible")]
         public enum WriteEventErrorCode : int
         {
             // check mapping to runtime codes
@@ -435,8 +434,7 @@ namespace System.Diagnostics.Tracing
             if (val > 1)
                 return;
 
-            if (sessionList == null)
-                sessionList = new List<SessionInfo>(8);
+            sessionList ??= new List<SessionInfo>(8);
 
             if (val == 1)
             {
@@ -684,7 +682,6 @@ namespace System.Diagnostics.Tracing
             return false;
         }
 
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1024:UsePropertiesWhereAppropriate")]
         public static WriteEventErrorCode GetLastWriteEventError()
         {
             return s_returnCode;
@@ -957,8 +954,6 @@ namespace System.Diagnostics.Tracing
         // <UsesUnsafeCode Name="Local v7 of type: Char*" />
         // <ReferencesCritical Name="Method: EncodeObject(Object&, EventData*, Byte*):String" Ring="1" />
         // </SecurityKernel>
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Maintainability", "CA1502:AvoidExcessiveComplexity", Justification = "Performance-critical code")]
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1045:DoNotPassTypesByReference")]
         internal unsafe bool WriteEvent(ref EventDescriptor eventDescriptor, IntPtr eventHandle, Guid* activityID, Guid* childActivityID, params object?[] eventPayload)
         {
             WriteEventErrorCode status = WriteEventErrorCode.NoError;
@@ -1155,7 +1150,6 @@ namespace System.Diagnostics.Tracing
         // <SecurityKernel Critical="True" Ring="0">
         // <CallsSuppressUnmanagedCode Name="Interop.Advapi32.EventWrite(System.Int64,EventDescriptor&,System.UInt32,System.Void*):System.UInt32" />
         // </SecurityKernel>
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1045:DoNotPassTypesByReference")]
         protected internal unsafe bool WriteEvent(ref EventDescriptor eventDescriptor, IntPtr eventHandle, Guid* activityID, Guid* childActivityID, int dataCount, IntPtr data)
         {
             if (childActivityID != null)
@@ -1177,7 +1171,6 @@ namespace System.Diagnostics.Tracing
             return true;
         }
 
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1045:DoNotPassTypesByReference")]
         internal unsafe bool WriteEventRaw(
             ref EventDescriptor eventDescriptor,
             IntPtr eventHandle,
diff --git a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs
index 47839357e2c..c8e718c98a3 100644
--- a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/EventSource.cs
@@ -248,7 +248,6 @@ namespace System.Diagnostics.Tracing
         /// Returns true if the eventSource has been enabled at all. This is the preferred test
         /// to be performed before a relatively expensive EventSource operation.
         /// </summary>
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         public bool IsEnabled()
         {
             return m_eventSourceEnabled;
@@ -263,7 +262,6 @@ namespace System.Diagnostics.Tracing
         /// positives (but is always accurate when returning false).  EventSources are free to
         /// have additional filtering.
         /// </summary>
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         public bool IsEnabled(EventLevel level, EventKeywords keywords)
         {
             return IsEnabled(level, keywords, EventChannel.None);
@@ -279,7 +277,6 @@ namespace System.Diagnostics.Tracing
         /// positives (but is always accurate when returning false).  EventSources are free to
         /// have additional filtering.
         /// </summary>
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         public bool IsEnabled(EventLevel level, EventKeywords keywords, EventChannel channel)
         {
             if (!m_eventSourceEnabled)
@@ -743,14 +740,12 @@ namespace System.Diagnostics.Tracing
 
 #pragma warning disable 1591
         // optimized for common signatures (no args)
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId)
         {
             WriteEventCore(eventId, 0, null);
         }
 
         // optimized for common signatures (ints)
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, int arg1)
         {
             if (m_eventSourceEnabled)
@@ -763,7 +758,6 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, int arg1, int arg2)
         {
             if (m_eventSourceEnabled)
@@ -779,7 +773,6 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, int arg1, int arg2, int arg3)
         {
             if (m_eventSourceEnabled)
@@ -799,7 +792,6 @@ namespace System.Diagnostics.Tracing
         }
 
         // optimized for common signatures (longs)
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, long arg1)
         {
             if (m_eventSourceEnabled)
@@ -812,7 +804,6 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, long arg1, long arg2)
         {
             if (m_eventSourceEnabled)
@@ -828,7 +819,6 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, long arg1, long arg2, long arg3)
         {
             if (m_eventSourceEnabled)
@@ -848,12 +838,11 @@ namespace System.Diagnostics.Tracing
         }
 
         // optimized for common signatures (strings)
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, string? arg1)
         {
             if (m_eventSourceEnabled)
             {
-                if (arg1 == null) arg1 = "";
+                arg1 ??= "";
                 fixed (char* string1Bytes = arg1)
                 {
                     EventSource.EventData* descrs = stackalloc EventSource.EventData[1];
@@ -865,13 +854,12 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, string? arg1, string? arg2)
         {
             if (m_eventSourceEnabled)
             {
-                if (arg1 == null) arg1 = "";
-                if (arg2 == null) arg2 = "";
+                arg1 ??= "";
+                arg2 ??= "";
                 fixed (char* string1Bytes = arg1)
                 fixed (char* string2Bytes = arg2)
                 {
@@ -887,14 +875,13 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, string? arg1, string? arg2, string? arg3)
         {
             if (m_eventSourceEnabled)
             {
-                if (arg1 == null) arg1 = "";
-                if (arg2 == null) arg2 = "";
-                if (arg3 == null) arg3 = "";
+                arg1 ??= "";
+                arg2 ??= "";
+                arg3 ??= "";
                 fixed (char* string1Bytes = arg1)
                 fixed (char* string2Bytes = arg2)
                 fixed (char* string3Bytes = arg3)
@@ -915,12 +902,11 @@ namespace System.Diagnostics.Tracing
         }
 
         // optimized for common signatures (string and ints)
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, string? arg1, int arg2)
         {
             if (m_eventSourceEnabled)
             {
-                if (arg1 == null) arg1 = "";
+                arg1 ??= "";
                 fixed (char* string1Bytes = arg1)
                 {
                     EventSource.EventData* descrs = stackalloc EventSource.EventData[2];
@@ -935,12 +921,11 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, string? arg1, int arg2, int arg3)
         {
             if (m_eventSourceEnabled)
             {
-                if (arg1 == null) arg1 = "";
+                arg1 ??= "";
                 fixed (char* string1Bytes = arg1)
                 {
                     EventSource.EventData* descrs = stackalloc EventSource.EventData[3];
@@ -959,12 +944,11 @@ namespace System.Diagnostics.Tracing
         }
 
         // optimized for common signatures (string and longs)
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, string? arg1, long arg2)
         {
             if (m_eventSourceEnabled)
             {
-                if (arg1 == null) arg1 = "";
+                arg1 ??= "";
                 fixed (char* string1Bytes = arg1)
                 {
                     EventSource.EventData* descrs = stackalloc EventSource.EventData[2];
@@ -980,12 +964,11 @@ namespace System.Diagnostics.Tracing
         }
 
         // optimized for common signatures (long and string)
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, long arg1, string? arg2)
         {
             if (m_eventSourceEnabled)
             {
-                if (arg2 == null) arg2 = "";
+                arg2 ??= "";
                 fixed (char* string2Bytes = arg2)
                 {
                     EventSource.EventData* descrs = stackalloc EventSource.EventData[2];
@@ -1001,12 +984,11 @@ namespace System.Diagnostics.Tracing
         }
 
         // optimized for common signatures (int and string)
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, int arg1, string? arg2)
         {
             if (m_eventSourceEnabled)
             {
-                if (arg2 == null) arg2 = "";
+                arg2 ??= "";
                 fixed (char* string2Bytes = arg2)
                 {
                     EventSource.EventData* descrs = stackalloc EventSource.EventData[2];
@@ -1021,7 +1003,6 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, byte[]? arg1)
         {
             if (m_eventSourceEnabled)
@@ -1055,7 +1036,6 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, long arg1, byte[]? arg2)
         {
             if (m_eventSourceEnabled)
@@ -1163,7 +1143,7 @@ namespace System.Diagnostics.Tracing
         ///    {
         ///        if (IsEnabled())
         ///        {
-        ///            if (arg2 == null) arg2 = "";
+        ///            arg2 ??= "";
         ///            fixed (char* string2Bytes = arg2)
         ///            {
         ///                EventSource.EventData* descrs = stackalloc EventSource.EventData[2];
@@ -1196,7 +1176,7 @@ namespace System.Diagnostics.Tracing
         ///    {
         ///        if (IsEnabled())
         ///        {
-        ///            if (arg2 == null) arg2 = "";
+        ///            arg2 ??= "";
         ///            fixed (char* string2Bytes = arg2)
         ///            {
         ///                EventSource.EventData* descrs = stackalloc EventSource.EventData[2];
@@ -1305,7 +1285,6 @@ namespace System.Diagnostics.Tracing
         /// method signature. Even if you use this for rare events, this call should be guarded by an <see cref="IsEnabled()"/>
         /// check so that the varargs call is not made when the EventSource is not active.
         /// </summary>
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         protected unsafe void WriteEvent(int eventId, params object?[] args)
         {
             WriteEventVarargs(eventId, null, args);
@@ -1442,7 +1421,6 @@ namespace System.Diagnostics.Tracing
         /// "Log", such an exception would become a cached exception for the initialization of the static
         /// member, and any future access to the "Log" would throw the cached exception).
         /// </summary>
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1720:IdentifiersShouldNotContainTypeNames", MessageId = "guid")]
         private unsafe void Initialize(Guid eventSourceGuid, string eventSourceName, string[]? traits)
         {
             try
@@ -1527,8 +1505,7 @@ namespace System.Diagnostics.Tracing
             }
             catch (Exception e)
             {
-                if (m_constructionException == null)
-                    m_constructionException = e;
+                m_constructionException ??= e;
                 ReportOutOfBandMessage("ERROR: Exception during construction of EventSource " + Name + ": " + e.Message, true);
             }
 
@@ -1577,10 +1554,7 @@ namespace System.Diagnostics.Tracing
             /// </summary>
             public void Start()
             {
-                if (this.w == null)
-                {
-                    this.w = new uint[85];
-                }
+                this.w ??= new uint[85];
 
                 this.length = 0;
                 this.pos = 0;
@@ -2178,7 +2152,6 @@ namespace System.Diagnostics.Tracing
             }
         }
 
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         private unsafe void WriteEventString(EventLevel level, long keywords, string msgString)
         {
 #if FEATURE_MANAGED_ETW
@@ -2658,7 +2631,9 @@ namespace System.Diagnostics.Tracing
                 {
                     // We can't do the command, simply remember it and we do it when we are fully constructed.
                     if (m_deferredCommands == null)
+                    {
                         m_deferredCommands = commandArgs;       // create the first entry
+                    }
                     else
                     {
                         // We have one or more entries, find the last one and add it to that.
@@ -2706,8 +2681,7 @@ namespace System.Diagnostics.Tracing
                     throw new ArgumentException(SR.EventSource_ListenerNotFound);
                 }
 
-                if (commandArgs.Arguments == null)
-                    commandArgs.Arguments = new Dictionary<string, string?>();
+                commandArgs.Arguments ??= new Dictionary<string, string?>();
 
                 if (commandArgs.Command == EventCommand.Update)
                 {
@@ -2944,8 +2918,7 @@ namespace System.Diagnostics.Tracing
                 EventDispatcher? dispatcher = m_Dispatchers;
                 while (dispatcher != null)
                 {
-                    if (dispatcher.m_EventEnabled == null)
-                        dispatcher.m_EventEnabled = new bool[m_eventData.Length];
+                    dispatcher.m_EventEnabled ??= new bool[m_eventData.Length];
                     dispatcher = dispatcher.m_Next;
                 }
 #if FEATURE_PERFTRACING
@@ -3683,8 +3656,7 @@ namespace System.Diagnostics.Tracing
             //     throw new WarningException(SR.EventSource_EventNameDoesNotEqualTaskPlusOpcode);
             // }
 
-            if (eventsByName == null)
-                eventsByName = new Dictionary<string, string>();
+            eventsByName ??= new Dictionary<string, string>();
 
             if (eventsByName.ContainsKey(evtName))
             {
@@ -3706,7 +3678,6 @@ namespace System.Diagnostics.Tracing
         /// </summary>
         /// <param name="method">The method to probe.</param>
         /// <returns>The literal value or -1 if the value could not be determined. </returns>
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Maintainability", "CA1502:AvoidExcessiveComplexity", Justification = "Switch statement is clearer than alternatives")]
         private static int GetHelperCallFirstArg(MethodInfo method)
         {
 #if (!ES_BUILD_PCL && !ES_BUILD_PN)
@@ -3835,7 +3806,6 @@ namespace System.Diagnostics.Tracing
         /// It will do this even if the EventSource is not enabled.
         /// TODO remove flush parameter it is not used.
         /// </summary>
-        [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "This does not need to be correct when racing with other threads")]
         internal void ReportOutOfBandMessage(string msg, bool flush)
         {
             try
@@ -4083,7 +4053,6 @@ namespace System.Diagnostics.Tracing
         /// call Dispose when they are done with their logging.
         /// </summary>
 #if ES_BUILD_STANDALONE
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1063:ImplementIDisposableCorrectly")]
 #endif
         public virtual void Dispose()
         {
@@ -4263,8 +4232,7 @@ namespace System.Diagnostics.Tracing
         {
             lock (EventListenersLock)
             {
-                if (s_EventSources == null)
-                    s_EventSources = new List<WeakReference>(2);
+                s_EventSources ??= new List<WeakReference>(2);
 
                 if (!s_EventSourceShutdownRegistered)
                 {
@@ -5380,8 +5348,10 @@ namespace System.Diagnostics.Tracing
                     ManifestError(SR.Format(SR.EventSource_OpcodeCollision, name, prevName, value));
                 }
             }
+
             opcodeTab[value] = name;
         }
+
         public void AddTask(string name, int value)
         {
             if ((flags & EventManifestOptions.Strict) != 0)
@@ -5396,10 +5366,11 @@ namespace System.Diagnostics.Tracing
                     ManifestError(SR.Format(SR.EventSource_TaskCollision, name, prevName, value));
                 }
             }
-            if (taskTab == null)
-                taskTab = new Dictionary<int, string>();
+
+            taskTab ??= new Dictionary<int, string>();
             taskTab[value] = name;
         }
+
         public void AddKeyword(string name, ulong value)
         {
             if ((value & (value - 1)) != 0)   // Is it a power of 2?
@@ -5418,8 +5389,8 @@ namespace System.Diagnostics.Tracing
                     ManifestError(SR.Format(SR.EventSource_KeywordCollision, name, prevName, "0x" + value.ToString("x", CultureInfo.CurrentCulture)));
                 }
             }
-            if (keywordTab == null)
-                keywordTab = new Dictionary<ulong, string>();
+
+            keywordTab ??= new Dictionary<ulong, string>();
             keywordTab[value] = name;
         }
 
@@ -5445,8 +5416,7 @@ namespace System.Diagnostics.Tracing
 
             ulong kwd = GetChannelKeyword(chValue);
 
-            if (channelTab == null)
-                channelTab = new Dictionary<int, ChannelInfo>(4);
+            channelTab ??= new Dictionary<int, ChannelInfo>(4);
             channelTab[value] = new ChannelInfo { Name = name, Keywords = kwd, Attribs = channelAttribute };
         }
 
@@ -5535,8 +5505,7 @@ namespace System.Diagnostics.Tracing
             {
                 // mark this index as "extraneous" (it has no parallel in the managed signature)
                 // we use these values in TranslateToManifestConvention()
-                if (byteArrArgIndices == null)
-                    byteArrArgIndices = new List<int>(4);
+                byteArrArgIndices ??= new List<int>(4);
                 byteArrArgIndices.Add(numParams);
 
                 // add an extra field to the template representing the length of the binary blob
@@ -5556,8 +5525,7 @@ namespace System.Diagnostics.Tracing
             if (type.IsEnum() && Enum.GetUnderlyingType(type) != typeof(ulong) && Enum.GetUnderlyingType(type) != typeof(long))
             {
                 templates.Append(" map=\"").Append(type.Name).Append("\"");
-                if (mapsTab == null)
-                    mapsTab = new Dictionary<string, Type>();
+                mapsTab ??= new Dictionary<string, Type>();
                 if (!mapsTab.ContainsKey(type.Name))
                     mapsTab.Add(type.Name, type);        // Remember that we need to dump the type enumeration
             }
@@ -5606,10 +5574,7 @@ namespace System.Diagnostics.Tracing
         {
             // strip off any non-channel keywords, since we are only interested in channels here.
             channelKeyword &= ValidPredefinedChannelKeywords;
-            if (channelTab == null)
-            {
-                channelTab = new Dictionary<int, ChannelInfo>(4);
-            }
+            channelTab ??= new Dictionary<int, ChannelInfo>(4);
 
             if (channelTab.Count == MaxCountChannels)
                 ManifestError(SR.EventSource_MaxChannelExceeded);
@@ -5697,8 +5662,8 @@ namespace System.Diagnostics.Tracing
                         access = attribs.Access;
 #endif
                     }
-                    if (fullName == null)
-                        fullName = providerName + "/" + channelInfo.Name;
+
+                    fullName ??= providerName + "/" + channelInfo.Name;
 
                     sb.Append("  <").Append(elementName);
                     sb.Append(" chid=\"").Append(channelInfo.Name).Append("\"");
@@ -5949,8 +5914,7 @@ namespace System.Diagnostics.Tracing
 
                 // allow channels to be auto-defined.  The well known ones get their well known names, and the
                 // rest get names Channel<N>.  This allows users to modify the Manifest if they want more advanced features.
-                if (channelTab == null)
-                    channelTab = new Dictionary<int, ChannelInfo>(4);
+                channelTab ??= new Dictionary<int, ChannelInfo>(4);
 
                 string channelName = channel.ToString();        // For well know channels this is a nice name, otherwise a number
                 if (EventChannel.Debug < channel)
@@ -5961,8 +5925,8 @@ namespace System.Diagnostics.Tracing
                     ManifestError(SR.Format(SR.EventSource_UndefinedChannel, channel, eventName));
             }
             // events that specify admin channels *must* have non-null "Message" attributes
-            if (resources != null && eventMessage == null)
-                eventMessage = resources.GetString("event_" + eventName, CultureInfo.InvariantCulture);
+            if (resources != null)
+                eventMessage ??= resources.GetString("event_" + eventName, CultureInfo.InvariantCulture);
 
             Debug.Assert(info!.Attribs != null);
             if (info.Attribs.EventChannelType == EventChannelType.Admin && eventMessage == null)
@@ -5976,8 +5940,7 @@ namespace System.Diagnostics.Tracing
                 return "";
 
             string? ret;
-            if (taskTab == null)
-                taskTab = new Dictionary<int, string>();
+            taskTab ??= new Dictionary<int, string>();
             if (!taskTab.TryGetValue((int)task, out ret))
                 ret = taskTab[(int)task] = eventName;
             return ret;
@@ -6108,8 +6071,7 @@ namespace System.Diagnostics.Tracing
 
         private static void UpdateStringBuilder([NotNull] ref StringBuilder? stringBuilder, string eventMessage, int startIndex, int count)
         {
-            if (stringBuilder == null)
-                stringBuilder = new StringBuilder();
+            stringBuilder ??= new StringBuilder();
             stringBuilder.Append(eventMessage, startIndex, count);
         }
 
diff --git a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/FrameworkEventSource.cs b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/FrameworkEventSource.cs
index 3ef69b03685..321ae819f50 100644
--- a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/FrameworkEventSource.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/FrameworkEventSource.cs
@@ -37,7 +37,7 @@ namespace System.Diagnostics.Tracing
         {
             if (IsEnabled())
             {
-                if (arg3 == null) arg3 = "";
+                arg3 ??= "";
                 fixed (char* string3Bytes = arg3)
                 {
                     EventSource.EventData* descrs = stackalloc EventSource.EventData[6];
@@ -70,7 +70,7 @@ namespace System.Diagnostics.Tracing
         {
             if (IsEnabled())
             {
-                if (arg3 == null) arg3 = "";
+                arg3 ??= "";
                 fixed (char* string3Bytes = arg3)
                 {
                     EventSource.EventData* descrs = stackalloc EventSource.EventData[3];
diff --git a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/TraceLogging/TraceLoggingTypeInfo.cs b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/TraceLogging/TraceLoggingTypeInfo.cs
index a34675facac..a5de12342d1 100644
--- a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/TraceLogging/TraceLoggingTypeInfo.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/TraceLogging/TraceLoggingTypeInfo.cs
@@ -162,13 +162,12 @@ namespace System.Diagnostics.Tracing
 
         public static TraceLoggingTypeInfo GetInstance(Type type, List<Type>? recursionCheck)
         {
-            Dictionary<Type, TraceLoggingTypeInfo> cache = threadCache ?? (threadCache = new Dictionary<Type, TraceLoggingTypeInfo>());
+            Dictionary<Type, TraceLoggingTypeInfo> cache = threadCache ??= new Dictionary<Type, TraceLoggingTypeInfo>();
 
             TraceLoggingTypeInfo? instance;
             if (!cache.TryGetValue(type, out instance))
             {
-                if (recursionCheck == null)
-                    recursionCheck = new List<Type>();
+                recursionCheck ??= new List<Type>();
                 int recursionCheckCount = recursionCheck.Count;
                 instance = Statics.CreateDefaultTypeInfo(type, recursionCheck);
                 cache[type] = instance;
diff --git a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/Winmeta.cs b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/Winmeta.cs
index a230f541ee4..03d86f8efab 100644
--- a/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/Winmeta.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Diagnostics/Tracing/Winmeta.cs
@@ -117,7 +117,6 @@ namespace System.Diagnostics.Tracing
     /// <summary>
     /// EventChannel. Custom values must be in the range from 16 through 255. Currently only predefined values allowed.
     /// </summary>
-    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1028:EnumStorageShouldBeInt32", Justification = "Backwards compatibility")]
     public enum EventChannel : byte
     {
         /// <summary>
diff --git a/netcore/System.Private.CoreLib/shared/System/Exception.cs b/netcore/System.Private.CoreLib/shared/System/Exception.cs
index 0fe895c2b8b..5e4f0789010 100644
--- a/netcore/System.Private.CoreLib/shared/System/Exception.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Exception.cs
@@ -87,7 +87,7 @@ namespace System
 
         public virtual string? Source
         {
-            get => _source ?? (_source = CreateSourceName());
+            get => _source ??= CreateSourceName();
             set => _source = value;
         }
 
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/CalendarData.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/CalendarData.cs
index 88e47bac81c..997cfb406e4 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/CalendarData.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/CalendarData.cs
@@ -112,23 +112,23 @@ namespace System.Globalization
 
                 // Something failed, try invariant for missing parts
                 // This is really not good, but we don't want the callers to crash.
-                if (this.sNativeName == null) this.sNativeName = string.Empty;           // Calendar Name for the locale.
+                this.sNativeName ??= string.Empty;           // Calendar Name for the locale.
 
                 // Formats
-                if (this.saShortDates == null) this.saShortDates = Invariant.saShortDates; // Short Data format, default first
-                if (this.saYearMonths == null) this.saYearMonths = Invariant.saYearMonths; // Year/Month Data format, default first
-                if (this.saLongDates == null) this.saLongDates = Invariant.saLongDates;  // Long Data format, default first
-                if (this.sMonthDay == null) this.sMonthDay = Invariant.sMonthDay;    // Month/Day format
+                this.saShortDates ??= Invariant.saShortDates; // Short Data format, default first
+                this.saYearMonths ??= Invariant.saYearMonths; // Year/Month Data format, default first
+                this.saLongDates ??= Invariant.saLongDates;  // Long Data format, default first
+                this.sMonthDay ??= Invariant.sMonthDay;    // Month/Day format
 
                 // Calendar Parts Names
-                if (this.saEraNames == null) this.saEraNames = Invariant.saEraNames;              // Names of Eras
-                if (this.saAbbrevEraNames == null) this.saAbbrevEraNames = Invariant.saAbbrevEraNames;        // Abbreviated Era Names
-                if (this.saAbbrevEnglishEraNames == null) this.saAbbrevEnglishEraNames = Invariant.saAbbrevEnglishEraNames; // Abbreviated Era Names in English
-                if (this.saDayNames == null) this.saDayNames = Invariant.saDayNames;              // Day Names, null to use locale data, starts on Sunday
-                if (this.saAbbrevDayNames == null) this.saAbbrevDayNames = Invariant.saAbbrevDayNames;        // Abbrev Day Names, null to use locale data, starts on Sunday
-                if (this.saSuperShortDayNames == null) this.saSuperShortDayNames = Invariant.saSuperShortDayNames;    // Super short Day of week names
-                if (this.saMonthNames == null) this.saMonthNames = Invariant.saMonthNames;            // Month Names (13)
-                if (this.saAbbrevMonthNames == null) this.saAbbrevMonthNames = Invariant.saAbbrevMonthNames;      // Abbrev Month Names (13)
+                this.saEraNames ??= Invariant.saEraNames;              // Names of Eras
+                this.saAbbrevEraNames ??= Invariant.saAbbrevEraNames;        // Abbreviated Era Names
+                this.saAbbrevEnglishEraNames ??= Invariant.saAbbrevEnglishEraNames; // Abbreviated Era Names in English
+                this.saDayNames ??= Invariant.saDayNames;              // Day Names, null to use locale data, starts on Sunday
+                this.saAbbrevDayNames ??= Invariant.saAbbrevDayNames;        // Abbrev Day Names, null to use locale data, starts on Sunday
+                this.saSuperShortDayNames ??= Invariant.saSuperShortDayNames;    // Super short Day of week names
+                this.saMonthNames ??= Invariant.saMonthNames;            // Month Names (13)
+                this.saAbbrevMonthNames ??= Invariant.saAbbrevMonthNames;      // Abbrev Month Names (13)
                 // Genitive and Leap names can follow the fallback below
             }
 
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/CultureData.Windows.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/CultureData.Windows.cs
index b8cb91b50ac..6c1902c7162 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/CultureData.Windows.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/CultureData.Windows.cs
@@ -379,8 +379,7 @@ namespace System.Globalization
                         {
                             // Found another ', so we have ''.  Need to add \' instead.
                             // 1st make sure we have our stringbuilder
-                            if (result == null)
-                                result = new StringBuilder(str, 0, i, str.Length * 2);
+                            result ??= new StringBuilder(str, 0, i, str.Length * 2);
 
                             // Append a \' and keep going (so we don't turn off quote mode)
                             result.Append("\\'");
@@ -402,8 +401,7 @@ namespace System.Globalization
                 {
                     // Found a \, need to change it to \\
                     // 1st make sure we have our stringbuilder
-                    if (result == null)
-                        result = new StringBuilder(str, 0, i, str.Length * 2);
+                    result ??= new StringBuilder(str, 0, i, str.Length * 2);
 
                     // Append our \\ to the string & continue
                     result.Append("\\\\");
@@ -411,8 +409,7 @@ namespace System.Globalization
                 }
 
                 // If we have a builder we need to add our character
-                if (result != null)
-                    result.Append(str[i]);
+                result?.Append(str[i]);
             }
 
             // Unchanged string? , just return input string
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/CultureData.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/CultureData.cs
index 7963d84d2c2..de6f326b6f3 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/CultureData.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/CultureData.cs
@@ -1880,10 +1880,7 @@ namespace System.Globalization
             int calendarIndex = (int)calendarId - 1;
 
             // Have to have calendars
-            if (_calendars == null)
-            {
-                _calendars = new CalendarData[CalendarData.MAX_CALENDARS];
-            }
+            _calendars ??= new CalendarData[CalendarData.MAX_CALENDARS];
 
             // we need the following local variable to avoid returning null
             // when another thread creates a new array of CalendarData (above)
@@ -2157,16 +2154,10 @@ namespace System.Globalization
                 switch (str[i])
                 {
                     case '\'':
-                        if (result == null)
-                        {
-                            result = new StringBuilder(str, start, i - start, str.Length);
-                        }
+                        result ??= new StringBuilder(str, start, i - start, str.Length);
                         break;
                     case '\\':
-                        if (result == null)
-                        {
-                            result = new StringBuilder(str, start, i - start, str.Length);
-                        }
+                        result ??= new StringBuilder(str, start, i - start, str.Length);
                         ++i;
                         if (i < str.Length)
                         {
@@ -2174,10 +2165,7 @@ namespace System.Globalization
                         }
                         break;
                     default:
-                        if (result != null)
-                        {
-                            result.Append(str[i]);
-                        }
+                        result?.Append(str[i]);
                         break;
                 }
             }
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfo.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfo.cs
index 430b1bffb43..33302642924 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfo.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfo.cs
@@ -150,31 +150,11 @@ namespace System.Globalization
 
         private DateTimeFormatFlags formatFlags = DateTimeFormatFlags.NotInitialized;
 
-        private string CultureName => _name ?? (_name = _cultureData.CultureName);
+        private string CultureName => _name ??= _cultureData.CultureName;
 
-        private CultureInfo Culture
-        {
-            get
-            {
-                if (_cultureInfo == null)
-                {
-                    _cultureInfo = CultureInfo.GetCultureInfo(CultureName);
-                }
-                return _cultureInfo;
-            }
-        }
+        private CultureInfo Culture => _cultureInfo ??= CultureInfo.GetCultureInfo(CultureName);
 
-        private string LanguageName
-        {
-            get
-            {
-                if (_langName == null)
-                {
-                    _langName = _cultureData.TwoLetterISOLanguageName;
-                }
-                return _langName;
-            }
-        }
+        private string LanguageName => _langName ??= _cultureData.TwoLetterISOLanguageName;
 
         /// <summary>
         /// Create an array of string which contains the abbreviated day names.
@@ -1898,62 +1878,25 @@ namespace System.Globalization
 
         // Decimal separator used by positive TimeSpan pattern
         private string? _decimalSeparator;
-        internal string DecimalSeparator
-        {
-            get
-            {
-                if (_decimalSeparator == null)
-                {
-                    CultureData? cultureDataWithoutUserOverrides = _cultureData.UseUserOverride ?
-                        CultureData.GetCultureData(_cultureData.CultureName, false) :
-                        _cultureData;
-                    _decimalSeparator = new NumberFormatInfo(cultureDataWithoutUserOverrides).NumberDecimalSeparator;
-                }
-                return _decimalSeparator;
-            }
-        }
+        internal string DecimalSeparator =>
+            _decimalSeparator ??=
+            new NumberFormatInfo(_cultureData.UseUserOverride ? CultureData.GetCultureData(_cultureData.CultureName, false) : _cultureData).NumberDecimalSeparator;
 
         // Positive TimeSpan Pattern
         private string? _fullTimeSpanPositivePattern;
-        internal string FullTimeSpanPositivePattern
-        {
-            get
-            {
-                if (_fullTimeSpanPositivePattern == null)
-                {
-                    _fullTimeSpanPositivePattern = "d':'h':'mm':'ss'" + DecimalSeparator + "'FFFFFFF";
-                }
-                return _fullTimeSpanPositivePattern;
-            }
-        }
+        internal string FullTimeSpanPositivePattern =>
+            _fullTimeSpanPositivePattern ??= "d':'h':'mm':'ss'" + DecimalSeparator + "'FFFFFFF";
 
         // Negative TimeSpan Pattern
         private string? _fullTimeSpanNegativePattern;
-        internal string FullTimeSpanNegativePattern
-        {
-            get
-            {
-                if (_fullTimeSpanNegativePattern == null)
-                    _fullTimeSpanNegativePattern = "'-'" + FullTimeSpanPositivePattern;
-                return _fullTimeSpanNegativePattern;
-            }
-        }
+        internal string FullTimeSpanNegativePattern =>
+            _fullTimeSpanNegativePattern ??= "'-'" + FullTimeSpanPositivePattern;
 
         // Get suitable CompareInfo from current DTFI object.
-        internal CompareInfo CompareInfo
-        {
-            get
-            {
-                if (_compareInfo == null)
-                {
-                    // We use the regular GetCompareInfo here to make sure the created CompareInfo object is stored in the
-                    // CompareInfo cache. otherwise we would just create CompareInfo using _cultureData.
-                    _compareInfo = CompareInfo.GetCompareInfo(_cultureData.SortName);
-                }
-
-                return _compareInfo;
-            }
-        }
+        internal CompareInfo CompareInfo =>
+            // We use the regular GetCompareInfo here to make sure the created CompareInfo object is stored in the
+            // CompareInfo cache. otherwise we would just create CompareInfo using _cultureData.
+            _compareInfo ??= CompareInfo.GetCompareInfo(_cultureData.SortName);
 
         internal const DateTimeStyles InvalidDateTimeStyles = ~(DateTimeStyles.AllowLeadingWhite | DateTimeStyles.AllowTrailingWhite
                                                                | DateTimeStyles.AllowInnerWhite | DateTimeStyles.NoCurrentDateDefault
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs
index 269d0878601..e93ad3d930c 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeFormatInfoScanner.cs
@@ -214,10 +214,8 @@ namespace System.Globalization
 
                 if (KnownWords.TryGetValue(str, out _) == false)
                 {
-                    if (m_dateWords == null)
-                    {
-                        m_dateWords = new List<string>();
-                    }
+                    m_dateWords ??= new List<string>();
+
                     if (formatPostfix == "MMMM")
                     {
                         // Add the word into the ArrayList as "\xfffe" + real month postfix.
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeParse.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeParse.cs
index e2f754745d4..dcde531546e 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeParse.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/DateTimeParse.cs
@@ -5896,13 +5896,7 @@ new DS[] { DS.ERROR,  DS.TX_NNN,  DS.TX_NNN,  DS.TX_NNN,  DS.ERROR,   DS.ERROR,
         internal DTSubStringType type;
         internal int value;
 
-        internal char this[int relativeIndex]
-        {
-            get
-            {
-                return s[index + relativeIndex];
-            }
-        }
+        internal char this[int relativeIndex] => s[index + relativeIndex];
     }
 
     //
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/GregorianCalendar.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/GregorianCalendar.cs
index 57a38d5a19a..11c552a82fa 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/GregorianCalendar.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/GregorianCalendar.cs
@@ -39,10 +39,7 @@ namespace System.Globalization
         /// Internal method to provide a default intance of GregorianCalendar.
         /// Used by NLS+ implementation
         /// </summary>
-        internal static Calendar GetDefaultInstance()
-        {
-            return s_defaultInstance ?? (s_defaultInstance = new GregorianCalendar());
-        }
+        internal static Calendar GetDefaultInstance() => s_defaultInstance ??= new GregorianCalendar();
 
         public GregorianCalendar() : this(GregorianCalendarTypes.Localized)
         {
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.cs
index 3449a84b901..eae8fa0bc87 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.cs
@@ -84,10 +84,7 @@ namespace System.Globalization
         internal static volatile Calendar? s_defaultInstance;
         internal GregorianCalendarHelper _helper;
 
-        internal static Calendar GetDefaultInstance()
-        {
-            return s_defaultInstance ?? (s_defaultInstance = new JapaneseCalendar());
-        }
+        internal static Calendar GetDefaultInstance() => s_defaultInstance ??= new JapaneseCalendar();
 
         public JapaneseCalendar()
         {
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/TaiwanCalendar.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/TaiwanCalendar.cs
index edd599b5371..03003826dfa 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/TaiwanCalendar.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/TaiwanCalendar.cs
@@ -32,10 +32,7 @@ namespace System.Globalization
 
         private readonly GregorianCalendarHelper _helper;
 
-        internal static Calendar GetDefaultInstance()
-        {
-            return s_defaultInstance ?? (s_defaultInstance = new TaiwanCalendar());
-        }
+        internal static Calendar GetDefaultInstance() => s_defaultInstance ??= new TaiwanCalendar();
 
         private static readonly DateTime s_calendarMinValue = new DateTime(1912, 1, 1);
 
diff --git a/netcore/System.Private.CoreLib/shared/System/Globalization/TextInfo.cs b/netcore/System.Private.CoreLib/shared/System/Globalization/TextInfo.cs
index 7fe69d66481..4187c0df715 100644
--- a/netcore/System.Private.CoreLib/shared/System/Globalization/TextInfo.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Globalization/TextInfo.cs
@@ -126,7 +126,7 @@ namespace System.Globalization
         /// </summary>
         public virtual string ListSeparator
         {
-            get => _listSeparator ?? (_listSeparator = _cultureData.ListSeparator);
+            get => _listSeparator ??= _cultureData.ListSeparator;
             set
             {
                 if (value == null)
diff --git a/netcore/System.Private.CoreLib/shared/System/IO/BinaryReader.cs b/netcore/System.Private.CoreLib/shared/System/IO/BinaryReader.cs
index c33a7406b78..2b213fe63ca 100644
--- a/netcore/System.Private.CoreLib/shared/System/IO/BinaryReader.cs
+++ b/netcore/System.Private.CoreLib/shared/System/IO/BinaryReader.cs
@@ -148,10 +148,7 @@ namespace System.IO
                 posSav = _stream.Position;
             }
 
-            if (_charBytes == null)
-            {
-                _charBytes = new byte[MaxCharBytesSize];
-            }
+            _charBytes ??= new byte[MaxCharBytesSize];
 
             Span<char> singleChar = stackalloc char[1];
 
@@ -289,15 +286,8 @@ namespace System.IO
                 return string.Empty;
             }
 
-            if (_charBytes == null)
-            {
-                _charBytes = new byte[MaxCharBytesSize];
-            }
-
-            if (_charBuffer == null)
-            {
-                _charBuffer = new char[_maxCharsSize];
-            }
+            _charBytes ??= new byte[MaxCharBytesSize];
+            _charBuffer ??= new char[_maxCharsSize];
 
             StringBuilder? sb = null;
             do
@@ -409,10 +399,7 @@ namespace System.IO
                 }
                 else
                 {
-                    if (_charBytes == null)
-                    {
-                        _charBytes = new byte[MaxCharBytesSize];
-                    }
+                    _charBytes ??= new byte[MaxCharBytesSize];
 
                     if (numBytes > MaxCharBytesSize)
                     {
diff --git a/netcore/System.Private.CoreLib/shared/System/IO/FileLoadException.cs b/netcore/System.Private.CoreLib/shared/System/IO/FileLoadException.cs
index 30f02786ed9..cbecd390c3b 100644
--- a/netcore/System.Private.CoreLib/shared/System/IO/FileLoadException.cs
+++ b/netcore/System.Private.CoreLib/shared/System/IO/FileLoadException.cs
@@ -41,17 +41,7 @@ namespace System.IO
             FileName = fileName;
         }
 
-        public override string Message
-        {
-            get
-            {
-                if (_message == null)
-                {
-                    _message = FormatFileLoadExceptionMessage(FileName, HResult);
-                }
-                return _message;
-            }
-        }
+        public override string Message => _message ??= FormatFileLoadExceptionMessage(FileName, HResult);
 
         public string? FileName { get; }
         public string? FusionLog { get; }
@@ -71,8 +61,7 @@ namespace System.IO
 
             if (FusionLog != null)
             {
-                if (s == null)
-                    s = " ";
+                s ??= " ";
                 s += Environment.NewLine;
                 s += Environment.NewLine;
                 s += FusionLog;
diff --git a/netcore/System.Private.CoreLib/shared/System/IO/FileNotFoundException.cs b/netcore/System.Private.CoreLib/shared/System/IO/FileNotFoundException.cs
index dd152bec47d..a4d6e442d4e 100644
--- a/netcore/System.Private.CoreLib/shared/System/IO/FileNotFoundException.cs
+++ b/netcore/System.Private.CoreLib/shared/System/IO/FileNotFoundException.cs
@@ -85,8 +85,7 @@ namespace System.IO
 
             if (FusionLog != null)
             {
-                if (s == null)
-                    s = " ";
+                s ??= " ";
                 s += Environment.NewLine;
                 s += Environment.NewLine;
                 s += FusionLog;
diff --git a/netcore/System.Private.CoreLib/shared/System/IO/FileStreamCompletionSource.Win32.cs b/netcore/System.Private.CoreLib/shared/System/IO/FileStreamCompletionSource.Win32.cs
index db2cf4cd191..9de86d1a67d 100644
--- a/netcore/System.Private.CoreLib/shared/System/IO/FileStreamCompletionSource.Win32.cs
+++ b/netcore/System.Private.CoreLib/shared/System/IO/FileStreamCompletionSource.Win32.cs
@@ -77,8 +77,7 @@ namespace System.IO
                 // Quick check to make sure the IO hasn't completed
                 if (_overlapped != null)
                 {
-                    Action<object?>? cancelCallback = s_cancelCallback;
-                    if (cancelCallback == null) s_cancelCallback = cancelCallback = Cancel;
+                    Action<object?>? cancelCallback = s_cancelCallback ??= Cancel;
 
                     // Register the cancellation only if the IO hasn't completed
                     long packedResult = Interlocked.CompareExchange(ref _result, RegisteringCancellation, NoResult);
diff --git a/netcore/System.Private.CoreLib/shared/System/IO/Stream.cs b/netcore/System.Private.CoreLib/shared/System/IO/Stream.cs
index e53fc9f8ad6..f9e2ecb4698 100644
--- a/netcore/System.Private.CoreLib/shared/System/IO/Stream.cs
+++ b/netcore/System.Private.CoreLib/shared/System/IO/Stream.cs
@@ -645,8 +645,7 @@ namespace System.IO
                 {
                     _context = null;
 
-                    ContextCallback? invokeAsyncCallback = s_invokeAsyncCallback;
-                    if (invokeAsyncCallback == null) s_invokeAsyncCallback = invokeAsyncCallback = InvokeAsyncCallback; // benign race condition
+                    ContextCallback? invokeAsyncCallback = s_invokeAsyncCallback ??= InvokeAsyncCallback;
 
                     ExecutionContext.RunInternal(context, invokeAsyncCallback, this);
                 }
diff --git a/netcore/System.Private.CoreLib/shared/System/IO/StreamReader.cs b/netcore/System.Private.CoreLib/shared/System/IO/StreamReader.cs
index 9db4769817b..3fdfe77ae6e 100644
--- a/netcore/System.Private.CoreLib/shared/System/IO/StreamReader.cs
+++ b/netcore/System.Private.CoreLib/shared/System/IO/StreamReader.cs
@@ -812,11 +812,9 @@ namespace System.IO
                     }
                     i++;
                 } while (i < _charLen);
+
                 i = _charLen - _charPos;
-                if (sb == null)
-                {
-                    sb = new StringBuilder(i + 80);
-                }
+                sb ??= new StringBuilder(i + 80);
                 sb.Append(_charBuffer, _charPos, i);
             } while (ReadBuffer() > 0);
             return sb.ToString();
@@ -896,10 +894,7 @@ namespace System.IO
                 } while (i < tmpCharLen);
 
                 i = tmpCharLen - tmpCharPos;
-                if (sb == null)
-                {
-                    sb = new StringBuilder(i + 80);
-                }
+                sb ??= new StringBuilder(i + 80);
                 sb.Append(tmpCharBuffer, tmpCharPos, i);
             } while (await ReadBufferAsync().ConfigureAwait(false) > 0);
 
@@ -1330,7 +1325,6 @@ namespace System.IO
                 return -1;
             }
 
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
             public override int Read(char[] buffer, int index, int count)
             {
                 return 0;
diff --git a/netcore/System.Private.CoreLib/shared/System/LocalDataStoreSlot.cs b/netcore/System.Private.CoreLib/shared/System/LocalDataStoreSlot.cs
index 64648784581..592b8171d90 100644
--- a/netcore/System.Private.CoreLib/shared/System/LocalDataStoreSlot.cs
+++ b/netcore/System.Private.CoreLib/shared/System/LocalDataStoreSlot.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 
 namespace System
@@ -16,7 +17,7 @@ namespace System
 
         internal ThreadLocal<object?> Data { get; private set; }
 
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Security", "CA1821", Justification = "Finalizer preserved for compat, it is suppressed by the constructor.")]
+        [SuppressMessage("Microsoft.Security", "CA1821", Justification = "Finalizer preserved for compat, it is suppressed by the constructor.")]
         ~LocalDataStoreSlot()
         {
         }
diff --git a/netcore/System.Private.CoreLib/shared/System/MemoryExtensions.Fast.cs b/netcore/System.Private.CoreLib/shared/System/MemoryExtensions.Fast.cs
index 801c87fa490..a0286dc9864 100644
--- a/netcore/System.Private.CoreLib/shared/System/MemoryExtensions.Fast.cs
+++ b/netcore/System.Private.CoreLib/shared/System/MemoryExtensions.Fast.cs
@@ -227,8 +227,7 @@ namespace System
             if (source.Overlaps(destination))
                 throw new InvalidOperationException(SR.InvalidOperation_SpanOverlappedOperation);
 
-            if (culture == null)
-                culture = CultureInfo.CurrentCulture;
+            culture ??= CultureInfo.CurrentCulture;
 
             // Assuming that changing case does not affect length
             if (destination.Length < source.Length)
@@ -280,8 +279,7 @@ namespace System
             if (source.Overlaps(destination))
                 throw new InvalidOperationException(SR.InvalidOperation_SpanOverlappedOperation);
 
-            if (culture == null)
-                culture = CultureInfo.CurrentCulture;
+            culture ??= CultureInfo.CurrentCulture;
 
             // Assuming that changing case does not affect length
             if (destination.Length < source.Length)
diff --git a/netcore/System.Private.CoreLib/shared/System/Object.cs b/netcore/System.Private.CoreLib/shared/System/Object.cs
index 376bb5536f9..a8e12bc18d0 100644
--- a/netcore/System.Private.CoreLib/shared/System/Object.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Object.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Runtime.Versioning;
@@ -28,7 +29,7 @@ namespace System
         // Allow an object to free resources before the object is reclaimed by the GC.
         // This method's virtual slot number is hardcoded in runtimes. Do not add any virtual methods ahead of this.
         [NonVersionable]
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1821:RemoveEmptyFinalizers")]
+        [SuppressMessage("Microsoft.Performance", "CA1821:RemoveEmptyFinalizers")]
         ~Object()
         {
         }
diff --git a/netcore/System.Private.CoreLib/shared/System/ParamsArray.cs b/netcore/System.Private.CoreLib/shared/System/ParamsArray.cs
index 88277b3376d..9ab86fa5167 100644
--- a/netcore/System.Private.CoreLib/shared/System/ParamsArray.cs
+++ b/netcore/System.Private.CoreLib/shared/System/ParamsArray.cs
@@ -62,10 +62,7 @@ namespace System
 
         public int Length => _args.Length;
 
-        public object? this[int index]
-        {
-            get { return index == 0 ? _arg0 : GetAtSlow(index); }
-        }
+        public object? this[int index] => index == 0 ? _arg0 : GetAtSlow(index);
 
         private object? GetAtSlow(int index)
         {
diff --git a/netcore/System.Private.CoreLib/shared/System/Reflection/AssemblyName.cs b/netcore/System.Private.CoreLib/shared/System/Reflection/AssemblyName.cs
index 690c3b0fae8..32e9a074cb4 100644
--- a/netcore/System.Private.CoreLib/shared/System/Reflection/AssemblyName.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Reflection/AssemblyName.cs
@@ -165,12 +165,7 @@ namespace System.Reflection
 
         // The compressed version of the public key formed from a truncated hash.
         // Will throw a SecurityException if _publicKey is invalid
-        public byte[]? GetPublicKeyToken()
-        {
-            if (_publicKeyToken == null)
-                _publicKeyToken = ComputePublicKeyToken();
-            return _publicKeyToken;
-        }
+        public byte[]? GetPublicKeyToken() => _publicKeyToken ??= ComputePublicKeyToken();
 
         public void SetPublicKeyToken(byte[]? publicKeyToken)
         {
diff --git a/netcore/System.Private.CoreLib/shared/System/Resources/ResourceManager.Uap.cs b/netcore/System.Private.CoreLib/shared/System/Resources/ResourceManager.Uap.cs
index be4d7dd4edf..4c229820f55 100644
--- a/netcore/System.Private.CoreLib/shared/System/Resources/ResourceManager.Uap.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Resources/ResourceManager.Uap.cs
@@ -154,8 +154,7 @@ namespace System.Resources
             // an empty string. We may in fact fail earlier for another reason, but otherwise we will
             // throw a MissingManifestResourceException when GetString is called indicating that a
             // resW filename called "" could not be found.
-            if (reswFilename == null)
-                reswFilename = string.Empty;
+            reswFilename ??= string.Empty;
 
             // At this point it is important NOT to set _useUapResourceManagement to false
             // if the PRI file does not exist because we are now certain we need to load PRI
diff --git a/netcore/System.Private.CoreLib/shared/System/Resources/ResourceManager.cs b/netcore/System.Private.CoreLib/shared/System/Resources/ResourceManager.cs
index 7f486b39993..8d98b575b8e 100644
--- a/netcore/System.Private.CoreLib/shared/System/Resources/ResourceManager.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Resources/ResourceManager.cs
@@ -608,10 +608,7 @@ namespace System.Resources
             }
 #endif
 
-            if (culture == null)
-            {
-                culture = CultureInfo.CurrentUICulture;
-            }
+            culture ??= CultureInfo.CurrentUICulture;
 
             ResourceSet? last = GetFirstResourceSet(culture);
 
diff --git a/netcore/System.Private.CoreLib/shared/System/Resources/RuntimeResourceSet.cs b/netcore/System.Private.CoreLib/shared/System/Resources/RuntimeResourceSet.cs
index 2a9e2c548aa..76d1d4aac2b 100644
--- a/netcore/System.Private.CoreLib/shared/System/Resources/RuntimeResourceSet.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Resources/RuntimeResourceSet.cs
@@ -370,9 +370,9 @@ namespace System.Resources
                 if (!_haveReadFromReader)
                 {
                     // If necessary, init our case insensitive hash table.
-                    if (ignoreCase && _caseInsensitiveTable == null)
+                    if (ignoreCase)
                     {
-                        _caseInsensitiveTable = new Dictionary<string, ResourceLocator>(StringComparer.OrdinalIgnoreCase);
+                        _caseInsensitiveTable ??= new Dictionary<string, ResourceLocator>(StringComparer.OrdinalIgnoreCase);
                     }
 
                     if (_defaultReader == null)
diff --git a/netcore/System.Private.CoreLib/shared/System/Runtime/CompilerServices/ContractHelper.cs b/netcore/System.Private.CoreLib/shared/System/Runtime/CompilerServices/ContractHelper.cs
index f75ca12ef06..5adf4471e8f 100644
--- a/netcore/System.Private.CoreLib/shared/System/Runtime/CompilerServices/ContractHelper.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Runtime/CompilerServices/ContractHelper.cs
@@ -61,7 +61,7 @@ namespace System.Runtime.CompilerServices
                     if (eventArgs.Unwind)
                     {
                         // unwind
-                        if (innerException == null) { innerException = eventArgs.thrownDuringHandler; }
+                        innerException ??= eventArgs.thrownDuringHandler;
                         throw new ContractException(failureKind, displayMessage, userMessage, conditionText, innerException);
                     }
                 }
diff --git a/netcore/System.Private.CoreLib/shared/System/Runtime/CompilerServices/StrongBox.cs b/netcore/System.Private.CoreLib/shared/System/Runtime/CompilerServices/StrongBox.cs
index 02a21c37e71..bdee5189b3c 100644
--- a/netcore/System.Private.CoreLib/shared/System/Runtime/CompilerServices/StrongBox.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Runtime/CompilerServices/StrongBox.cs
@@ -16,7 +16,6 @@ namespace System.Runtime.CompilerServices
         /// Gets the strongly typed value associated with the <see cref = "StrongBox{T}"></see>
         /// <remarks>This is explicitly exposed as a field instead of a property to enable loading the address of the field.</remarks>
         /// </summary>
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1051:DoNotDeclareVisibleInstanceFields")]
         [MaybeNull] public T Value = default!;
 
         /// <summary>
diff --git a/netcore/System.Private.CoreLib/shared/System/Runtime/ConstrainedExecution/CriticalFinalizerObject.cs b/netcore/System.Private.CoreLib/shared/System/Runtime/ConstrainedExecution/CriticalFinalizerObject.cs
index 0f22b036328..a6e07b8e53d 100644
--- a/netcore/System.Private.CoreLib/shared/System/Runtime/ConstrainedExecution/CriticalFinalizerObject.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Runtime/ConstrainedExecution/CriticalFinalizerObject.cs
@@ -12,6 +12,8 @@
 **
 ===========================================================*/
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace System.Runtime.ConstrainedExecution
 {
     public abstract class CriticalFinalizerObject
@@ -20,7 +22,7 @@ namespace System.Runtime.ConstrainedExecution
         {
         }
 
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1821:RemoveEmptyFinalizers")]
+        [SuppressMessage("Microsoft.Performance", "CA1821:RemoveEmptyFinalizers")]
         ~CriticalFinalizerObject()
         {
         }
diff --git a/netcore/System.Private.CoreLib/shared/System/Runtime/InteropServices/SafeHandle.cs b/netcore/System.Private.CoreLib/shared/System/Runtime/InteropServices/SafeHandle.cs
index 234446ce480..c9f8766aecb 100644
--- a/netcore/System.Private.CoreLib/shared/System/Runtime/InteropServices/SafeHandle.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Runtime/InteropServices/SafeHandle.cs
@@ -23,7 +23,6 @@ namespace System.Runtime.InteropServices
         //   manipulating _state.
 
         /// <summary>Specifies the handle to be wrapped.</summary>
-        [SuppressMessage("Microsoft.Security", "CA2111:PointersShouldNotBeVisible")]
         protected IntPtr handle;
         /// <summary>Combined ref count and closed/disposed flags (so we can atomically modify them).</summary>
         private volatile int _state;
diff --git a/netcore/System.Private.CoreLib/shared/System/Runtime/Serialization/SerializationInfo.cs b/netcore/System.Private.CoreLib/shared/System/Runtime/Serialization/SerializationInfo.cs
index 83c27fb9236..200a4becfde 100644
--- a/netcore/System.Private.CoreLib/shared/System/Runtime/Serialization/SerializationInfo.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Runtime/Serialization/SerializationInfo.cs
@@ -34,15 +34,8 @@ namespace System.Runtime.Serialization
         [ThreadStatic]
         private static DeserializationTracker? t_deserializationTracker;
 
-        private static DeserializationTracker GetThreadDeserializationTracker()
-        {
-            if (t_deserializationTracker == null)
-            {
-                t_deserializationTracker = new DeserializationTracker();
-            }
-
-            return t_deserializationTracker;
-        }
+        private static DeserializationTracker GetThreadDeserializationTracker() =>
+            t_deserializationTracker ??= new DeserializationTracker();
 #endif // !CORECLR
 
         // Returns true if deserialization is currently in progress
diff --git a/netcore/System.Private.CoreLib/shared/System/RuntimeType.cs b/netcore/System.Private.CoreLib/shared/System/RuntimeType.cs
index 81cb7e7a03e..70cd615887f 100644
--- a/netcore/System.Private.CoreLib/shared/System/RuntimeType.cs
+++ b/netcore/System.Private.CoreLib/shared/System/RuntimeType.cs
@@ -82,10 +82,7 @@ namespace System
                 members = GetMember(defaultMemberName);
             }
 
-            if (members == null)
-                members = Array.Empty<MemberInfo>();
-
-            return members;
+            return members ?? Array.Empty<MemberInfo>();
         }
 
         public override Type GetElementType() => RuntimeTypeHandle.GetElementType(this);
diff --git a/netcore/System.Private.CoreLib/shared/System/Security/SecurityElement.cs b/netcore/System.Private.CoreLib/shared/System/Security/SecurityElement.cs
index 93d505615b1..3ebf72411f1 100644
--- a/netcore/System.Private.CoreLib/shared/System/Security/SecurityElement.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Security/SecurityElement.cs
@@ -245,8 +245,7 @@ namespace System.Security
             if (child == null)
                 throw new ArgumentNullException(nameof(child));
 
-            if (_children == null)
-                _children = new ArrayList(ChildrenTypical);
+            _children ??= new ArrayList(ChildrenTypical);
 
             _children.Add(child);
         }
@@ -405,8 +404,7 @@ namespace System.Security
                 }
                 else
                 {
-                    if (sb == null)
-                        sb = new StringBuilder();
+                    sb ??= new StringBuilder();
 
                     sb.Append(str, newIndex, index - newIndex);
                     sb.Append(GetEscapeSequence(str[index]));
@@ -470,8 +468,7 @@ namespace System.Security
                 }
                 else
                 {
-                    if (sb == null)
-                        sb = new StringBuilder();
+                    sb ??= new StringBuilder();
 
                     sb.Append(str, newIndex, index - newIndex);
                     sb.Append(GetUnescapeSequence(str, index, out newIndex)); // updates the newIndex too
diff --git a/netcore/System.Private.CoreLib/shared/System/String.Manipulation.cs b/netcore/System.Private.CoreLib/shared/System/String.Manipulation.cs
index 7944df5968f..0c79ce37c14 100644
--- a/netcore/System.Private.CoreLib/shared/System/String.Manipulation.cs
+++ b/netcore/System.Private.CoreLib/shared/System/String.Manipulation.cs
@@ -1000,8 +1000,7 @@ namespace System
 
             // If they asked to replace oldValue with a null, replace all occurrences
             // with the empty string.
-            if (newValue == null)
-                newValue = string.Empty;
+            newValue ??= string.Empty;
 
             CultureInfo referenceCulture = culture ?? CultureInfo.CurrentCulture;
             StringBuilder result = StringBuilderCache.Acquire();
@@ -1119,8 +1118,7 @@ namespace System
                 throw new ArgumentException(SR.Argument_StringZeroLength, nameof(oldValue));
 
             // Api behavior: if newValue is null, instances of oldValue are to be removed.
-            if (newValue == null)
-                newValue = string.Empty;
+            newValue ??= string.Empty;
 
             Span<int> initialSpan = stackalloc int[StackallocIntBufferSizeLimit];
             var replacementIndices = new ValueListBuilder<int>(initialSpan);
diff --git a/netcore/System.Private.CoreLib/shared/System/Text/DecoderBestFitFallback.cs b/netcore/System.Private.CoreLib/shared/System/Text/DecoderBestFitFallback.cs
index 7991419f698..ad47a58067d 100644
--- a/netcore/System.Private.CoreLib/shared/System/Text/DecoderBestFitFallback.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Text/DecoderBestFitFallback.cs
@@ -71,8 +71,7 @@ namespace System.Text
                 lock (InternalSyncObject)
                 {
                     // Double check before we do it again.
-                    if (_oFallback._arrayBestFit == null)
-                        _oFallback._arrayBestFit = fallback._encoding.GetBestFitBytesToUnicodeData();
+                    _oFallback._arrayBestFit ??= fallback._encoding.GetBestFitBytesToUnicodeData();
                 }
             }
         }
diff --git a/netcore/System.Private.CoreLib/shared/System/Text/EncoderBestFitFallback.cs b/netcore/System.Private.CoreLib/shared/System/Text/EncoderBestFitFallback.cs
index 33df140e670..d3b24e1d91a 100644
--- a/netcore/System.Private.CoreLib/shared/System/Text/EncoderBestFitFallback.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Text/EncoderBestFitFallback.cs
@@ -71,8 +71,7 @@ namespace System.Text
                 lock (InternalSyncObject)
                 {
                     // Double check before we do it again.
-                    if (_oFallback._arrayBestFit == null)
-                        _oFallback._arrayBestFit = fallback._encoding.GetBestFitUnicodeToBytesData();
+                    _oFallback._arrayBestFit ??= fallback._encoding.GetBestFitUnicodeToBytesData();
                 }
             }
         }
diff --git a/netcore/System.Private.CoreLib/shared/System/Text/StringBuilder.cs b/netcore/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
index 1300f16c360..becf7e12e99 100644
--- a/netcore/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
@@ -1781,9 +1781,9 @@ namespace System.Text
                     // Otherwise, fallback to trying IFormattable or calling ToString.
                     if (arg is IFormattable formattableArg)
                     {
-                        if (itemFormatSpan.Length != 0 && itemFormat == null)
+                        if (itemFormatSpan.Length != 0)
                         {
-                            itemFormat = new string(itemFormatSpan);
+                            itemFormat ??= new string(itemFormatSpan);
                         }
                         s = formattableArg.ToString(itemFormat, provider);
                     }
diff --git a/netcore/System.Private.CoreLib/shared/System/Threading/CancellationTokenSource.cs b/netcore/System.Private.CoreLib/shared/System/Threading/CancellationTokenSource.cs
index dec0eab801a..1ed5c02be63 100644
--- a/netcore/System.Private.CoreLib/shared/System/Threading/CancellationTokenSource.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Threading/CancellationTokenSource.cs
@@ -697,7 +697,7 @@ namespace System.Threading
                         catch (Exception ex) when (!throwOnFirstException)
                         {
                             // Store the exception and continue
-                            (exceptionList ?? (exceptionList = new List<Exception>())).Add(ex);
+                            (exceptionList ??= new List<Exception>()).Add(ex);
                         }
 
                         // Drop the node. While we could add it to the free list, doing so has cost (we'd need to take the lock again)
diff --git a/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs b/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
index dd8a36ebe2b..abbdc13c9de 100644
--- a/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
@@ -226,7 +226,7 @@ namespace System.Threading.Tasks
 
             // Store the faulted task's exceptions
             CompletionState cs = EnsureCompletionStateInitialized();
-            if (cs.m_exceptions == null) cs.m_exceptions = new List<Exception>();
+            cs.m_exceptions ??= new List<Exception>();
             cs.m_exceptions.AddRange(faultedTask.Exception.InnerExceptions);
 
             // Now that we're doomed, request completion
@@ -246,20 +246,15 @@ namespace System.Threading.Tasks
 
         /// <summary>Gets the number of tasks waiting to run concurrently.</summary>
         /// <remarks>This does not take the necessary lock, as it's only called from under the debugger.</remarks>
-        [SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
         private int ConcurrentTaskCountForDebugger => m_concurrentTaskScheduler.m_tasks.Count;
 
         /// <summary>Gets the number of tasks waiting to run exclusively.</summary>
         /// <remarks>This does not take the necessary lock, as it's only called from under the debugger.</remarks>
-        [SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
         private int ExclusiveTaskCountForDebugger => m_exclusiveTaskScheduler.m_tasks.Count;
 
         /// <summary>Notifies the pair that new work has arrived to be processed.</summary>
         /// <param name="fairly">Whether tasks should be scheduled fairly with regards to other tasks.</param>
         /// <remarks>Must only be called while holding the lock.</remarks>
-        [SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
-        [SuppressMessage("Microsoft.Performance", "CA1804:RemoveUnusedLocals")]
-        [SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope")]
         private void ProcessAsyncIfNecessary(bool fairly = false)
         {
             ContractAssertMonitorStatus(ValueLock, held: true);
@@ -344,7 +339,7 @@ namespace System.Threading.Tasks
         {
             if (TaskScheduler.Default == m_underlyingTaskScheduler)
             {
-                IThreadPoolWorkItem workItem = m_threadPoolWorkItem ?? (m_threadPoolWorkItem = new SchedulerWorkItem(this));
+                IThreadPoolWorkItem workItem = m_threadPoolWorkItem ??= new SchedulerWorkItem(this);
                 ThreadPool.UnsafeQueueUserWorkItemInternal(workItem, preferLocal: !fairly);
                 return true;
             }
@@ -467,7 +462,6 @@ namespace System.Threading.Tasks
         /// state in one of those conditions or if the user explicitly asks for
         /// the Completion.
         /// </summary>
-        [SuppressMessage("Microsoft.Performance", "CA1812:AvoidUninstantiatedInternalClasses")]
         private sealed class CompletionState : Task
         {
             /// <summary>Whether the scheduler has had completion requested.</summary>
@@ -622,7 +616,6 @@ namespace System.Threading.Tasks
             /// </summary>
             /// <param name="task">The task to execute inline if possible.</param>
             /// <returns>true if the task was inlined successfully; otherwise, false.</returns>
-            [SuppressMessage("Microsoft.Performance", "CA1804:RemoveUnusedLocals", MessageId = "ignored")]
             private bool TryExecuteTaskInlineOnTargetScheduler(Task task)
             {
                 // We'd like to simply call TryExecuteTaskInline here, but we can't.
@@ -669,7 +662,6 @@ namespace System.Threading.Tasks
             protected override IEnumerable<Task> GetScheduledTasks() { return m_tasks; }
 
             /// <summary>Gets the number of tasks queued to this scheduler.</summary>
-            [SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
             private int CountForDebugger => m_tasks.Count;
 
             /// <summary>Provides a debug view for ConcurrentExclusiveTaskScheduler.</summary>
diff --git a/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs b/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs
index 8b6632c9ee9..1cd12545156 100644
--- a/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs
@@ -1333,10 +1333,8 @@ namespace System.Threading.Tasks
         /// ASSUMES THAT m_stateFlags IS ALREADY SET!
         /// </summary>
         /// <returns>The initialized contingent properties object.</returns>
-        internal ContingentProperties EnsureContingentPropertiesInitializedUnsafe()
-        {
-            return m_contingentProperties ?? (m_contingentProperties = new ContingentProperties());
-        }
+        internal ContingentProperties EnsureContingentPropertiesInitializedUnsafe() =>
+            m_contingentProperties ??= new ContingentProperties();
 
         /// <summary>
         /// This internal property provides access to the CancellationToken that was set on the task
@@ -4777,7 +4775,7 @@ namespace System.Threading.Tasks
         /// <param name="initSize">The size to which to initialize the list if the list is null.</param>
         private static void AddToList<T>(T item, ref List<T>? list, int initSize)
         {
-            if (list == null) list = new List<T>(initSize);
+            list ??= new List<T>(initSize);
             list.Add(item);
         }
 
@@ -4863,11 +4861,7 @@ namespace System.Threading.Tasks
                 // this will make sure it won't throw again in the implicit wait
                 t.UpdateExceptionObservedStatus();
 
-                if (exceptions == null)
-                {
-                    exceptions = new List<Exception>(ex.InnerExceptions.Count);
-                }
-
+                exceptions ??= new List<Exception>(ex.InnerExceptions.Count);
                 exceptions.AddRange(ex.InnerExceptions);
             }
         }
@@ -5690,12 +5684,12 @@ namespace System.Threading.Tasks
 
                         if (task.IsFaulted)
                         {
-                            if (observedExceptions == null) observedExceptions = new List<ExceptionDispatchInfo>();
+                            observedExceptions ??= new List<ExceptionDispatchInfo>();
                             observedExceptions.AddRange(task.GetExceptionDispatchInfos());
                         }
                         else if (task.IsCanceled)
                         {
-                            if (canceledTask == null) canceledTask = task; // use the first task that's canceled
+                            canceledTask ??= task; // use the first task that's canceled
                         }
 
                         // Regardless of completion state, if the task has its debug bit set, transfer it to the
@@ -5924,12 +5918,12 @@ namespace System.Threading.Tasks
 
                         if (task.IsFaulted)
                         {
-                            if (observedExceptions == null) observedExceptions = new List<ExceptionDispatchInfo>();
+                            observedExceptions ??= new List<ExceptionDispatchInfo>();
                             observedExceptions.AddRange(task.GetExceptionDispatchInfos());
                         }
                         else if (task.IsCanceled)
                         {
-                            if (canceledTask == null) canceledTask = task; // use the first task that's canceled
+                            canceledTask ??= task; // use the first task that's canceled
                         }
                         else
                         {
diff --git a/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/TaskContinuation.cs b/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/TaskContinuation.cs
index 985357731a8..684d2bf4857 100644
--- a/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/TaskContinuation.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Threading/Tasks/TaskContinuation.cs
@@ -437,12 +437,7 @@ namespace System.Threading.Tasks
         /// to be passed as state.
         /// </returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static ContextCallback GetPostActionCallback()
-        {
-            ContextCallback? callback = s_postActionCallback;
-            if (callback == null) { s_postActionCallback = callback = PostAction; } // lazily initialize SecurityCritical delegate
-            return callback;
-        }
+        private static ContextCallback GetPostActionCallback() => s_postActionCallback ??= PostAction;
     }
 
     /// <summary>Task continuation for awaiting with a task scheduler.</summary>
diff --git a/netcore/System.Private.CoreLib/shared/System/Threading/ThreadPool.cs b/netcore/System.Private.CoreLib/shared/System/Threading/ThreadPool.cs
index 8ab07b7774d..8f99a522be4 100644
--- a/netcore/System.Private.CoreLib/shared/System/Threading/ThreadPool.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Threading/ThreadPool.cs
@@ -212,7 +212,6 @@ namespace System.Threading
                 }
             }
 
-            [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "Reviewed for thread safety")]
             public bool LocalFindAndPop(object obj)
             {
                 // Fast path: check the tail. If equal, we can skip the lock.
@@ -271,7 +270,6 @@ namespace System.Threading
 
             public object? LocalPop() => m_headIndex < m_tailIndex ? LocalPopCore() : null;
 
-            [SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "Reviewed for thread safety")]
             private object? LocalPopCore()
             {
                 while (true)
diff --git a/netcore/System.Private.CoreLib/shared/System/Threading/TimerQueue.Portable.cs b/netcore/System.Private.CoreLib/shared/System/Threading/TimerQueue.Portable.cs
index 587eaca77af..2e47b71aa01 100644
--- a/netcore/System.Private.CoreLib/shared/System/Threading/TimerQueue.Portable.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Threading/TimerQueue.Portable.cs
@@ -33,10 +33,7 @@ namespace System.Threading
             Debug.Assert(s_scheduledTimers == null);
 
             var timers = new List<TimerQueue>(Instances.Length);
-            if (s_scheduledTimersToFire == null)
-            {
-                s_scheduledTimersToFire = new List<TimerQueue>(Instances.Length);
-            }
+            s_scheduledTimersToFire ??= new List<TimerQueue>(Instances.Length);
 
             Thread timerThread = new Thread(TimerThread);
             timerThread.IsBackground = true;
diff --git a/netcore/System.Private.CoreLib/shared/System/TimeZone.cs b/netcore/System.Private.CoreLib/shared/System/TimeZone.cs
index c9b0c3272d8..c58f3259e38 100644
--- a/netcore/System.Private.CoreLib/shared/System/TimeZone.cs
+++ b/netcore/System.Private.CoreLib/shared/System/TimeZone.cs
@@ -59,14 +59,12 @@ namespace System
                 {
                     lock (InternalSyncObject)
                     {
-                        if (currentTimeZone == null)
-                        {
-                            currentTimeZone = new CurrentSystemTimeZone();
-                        }
+                        currentTimeZone ??= new CurrentSystemTimeZone();
                         tz = currentTimeZone;
                     }
                 }
-                return (tz);
+
+                return tz;
             }
         }
 
diff --git a/netcore/System.Private.CoreLib/shared/System/TimeZoneInfo.Unix.cs b/netcore/System.Private.CoreLib/shared/System/TimeZoneInfo.Unix.cs
index 1321fe768ec..584db1d7445 100644
--- a/netcore/System.Private.CoreLib/shared/System/TimeZoneInfo.Unix.cs
+++ b/netcore/System.Private.CoreLib/shared/System/TimeZoneInfo.Unix.cs
@@ -488,10 +488,7 @@ namespace System
                                 // we're returning directories.
                                 if (isDir)
                                 {
-                                    if (toExplore == null)
-                                    {
-                                        toExplore = new List<string>();
-                                    }
+                                    toExplore ??= new List<string>();
                                     toExplore.Add(fullPath);
                                 }
                                 else if (condition(fullPath))
diff --git a/netcore/System.Private.CoreLib/shared/System/Tuple.cs b/netcore/System.Private.CoreLib/shared/System/Tuple.cs
index 8ef95d2f673..17d9fd98752 100644
--- a/netcore/System.Private.CoreLib/shared/System/Tuple.cs
+++ b/netcore/System.Private.CoreLib/shared/System/Tuple.cs
@@ -292,18 +292,13 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     [Serializable]
@@ -409,19 +404,14 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     [Serializable]
@@ -536,20 +526,15 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     [Serializable]
@@ -673,21 +658,16 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    4 => Item5,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                4 => Item5,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     [Serializable]
@@ -820,22 +800,17 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    4 => Item5,
-                    5 => Item6,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                4 => Item5,
+                5 => Item6,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     [Serializable]
@@ -977,23 +952,18 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    4 => Item5,
-                    5 => Item6,
-                    6 => Item7,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                4 => Item5,
+                5 => Item6,
+                6 => Item7,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     [Serializable]
@@ -1171,23 +1141,18 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    4 => Item5,
-                    5 => Item6,
-                    6 => Item7,
-
-                    _ => ((ITupleInternal)Rest)[index - 7],
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                4 => Item5,
+                5 => Item6,
+                6 => Item7,
+
+                _ => ((ITupleInternal)Rest)[index - 7],
+            };
     }
 }
diff --git a/netcore/System.Private.CoreLib/shared/System/ValueTuple.cs b/netcore/System.Private.CoreLib/shared/System/ValueTuple.cs
index 749d172f503..9792b840a80 100644
--- a/netcore/System.Private.CoreLib/shared/System/ValueTuple.cs
+++ b/netcore/System.Private.CoreLib/shared/System/ValueTuple.cs
@@ -137,13 +137,7 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
-            {
-                throw new IndexOutOfRangeException();
-            }
-        }
+        object? ITuple.this[int index] => throw new IndexOutOfRangeException();
 
         /// <summary>Creates a new struct 0-tuple.</summary>
         /// <returns>A 0-tuple.</returns>
@@ -654,18 +648,13 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     /// <summary>
@@ -857,19 +846,14 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     /// <summary>
@@ -1078,20 +1062,15 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     /// <summary>
@@ -1317,21 +1296,16 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    4 => Item5,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                4 => Item5,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     /// <summary>
@@ -1574,22 +1548,17 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    4 => Item5,
-                    5 => Item6,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                4 => Item5,
+                5 => Item6,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     /// <summary>
@@ -1849,23 +1818,18 @@ namespace System
         /// <summary>
         /// Get the element at position <param name="index"/>.
         /// </summary>
-        object? ITuple.this[int index]
-        {
-            get
+        object? ITuple.this[int index] =>
+            index switch
             {
-                return index switch
-                {
-                    0 => Item1,
-                    1 => Item2,
-                    2 => Item3,
-                    3 => Item4,
-                    4 => Item5,
-                    5 => Item6,
-                    6 => Item7,
-                    _ => throw new IndexOutOfRangeException(),
-                };
-            }
-        }
+                0 => Item1,
+                1 => Item2,
+                2 => Item3,
+                3 => Item4,
+                4 => Item5,
+                5 => Item6,
+                6 => Item7,
+                _ => throw new IndexOutOfRangeException(),
+            };
     }
 
     /// <summary>