Changing Span to return default on null instead of throwing.

12 files changed, 130 insertions, 55 deletions

diff --git a/src/System.Memory/System.Memory.sln b/src/System.Memory/System.Memory.sln
index 402cbd12a0..7c68229780 100644
--- a/src/System.Memory/System.Memory.sln
+++ b/src/System.Memory/System.Memory.sln
@@ -1,6 +1,6 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 14
-VisualStudioVersion = 14.0.25420.1
+# Visual Studio 15
+VisualStudioVersion = 15.0.27331.1
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "System.Memory.Tests", "tests\System.Memory.Tests.csproj", "{15DB0DCC-68B4-4CFB-8BD2-F26BCCAF5A3F}"
 	ProjectSection(ProjectDependencies) = postProject
@@ -25,6 +25,13 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{E107E9C1-E89
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "ref", "ref", "{2E666815-2EDB-464B-9DF6-380BF4789AD4}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{3F794AE4-319F-4498-A9DA-C49A4EB11D9E}"
+	ProjectSection(SolutionItems) = preProject
+		..\Common\src\CoreLib\System\ReadOnlySpan.Fast.cs = ..\Common\src\CoreLib\System\ReadOnlySpan.Fast.cs
+		..\Common\src\CoreLib\System\Span.Fast.cs = ..\Common\src\CoreLib\System\Span.Fast.cs
+		..\Common\src\CoreLib\System\Span.NonGeneric.cs = ..\Common\src\CoreLib\System\Span.NonGeneric.cs
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -57,4 +64,7 @@ Global
 		{4BBC8F69-D03E-4432-AA8A-D458FA5B235A} = {E107E9C1-E893-4E87-987E-04EF0DCEAEFD}
 		{E883935B-D8FD-4FC9-A189-9D9E7F7EF550} = {2E666815-2EDB-464B-9DF6-380BF4789AD4}
 	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {D1974D36-E7EF-4503-B474-D92F2D79ABE5}
+	EndGlobalSection
 EndGlobal
diff --git a/src/System.Memory/src/System/MemoryExtensions.Fast.cs b/src/System.Memory/src/System/MemoryExtensions.Fast.cs
index 3ef952951b..2a540f43e8 100644
--- a/src/System.Memory/src/System/MemoryExtensions.Fast.cs
+++ b/src/System.Memory/src/System/MemoryExtensions.Fast.cs
@@ -43,7 +43,7 @@ namespace System
         /// Creates a new readonly span over the portion of the target string.
         /// </summary>
         /// <param name="text">The target string.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is null.</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         public static ReadOnlySpan<char> AsReadOnlySpan(this string text) => Span.AsReadOnlySpan(text);
 
         /// <summary>
@@ -63,7 +63,7 @@ namespace System
         /// <param name="text">The target string.</param>
         /// <param name="start">The index at which to begin this slice.</param>
         /// <param name="length">The desired length for the slice (exclusive).</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is null.</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> index or <paramref name="length"/> is not in range.
         /// </exception>
@@ -71,13 +71,13 @@ namespace System
 
         /// <summary>Creates a new <see cref="ReadOnlyMemory{T}"/> over the portion of the target string.</summary>
         /// <param name="text">The target string.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is a null reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         public static ReadOnlyMemory<char> AsReadOnlyMemory(this string text) => Span.AsReadOnlyMemory(text);
 
         /// <summary>Creates a new <see cref="ReadOnlyMemory{T}"/> over the portion of the target string.</summary>
         /// <param name="text">The target string.</param>
         /// <param name="start">The index at which to begin this slice.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is a null reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> index is not in range (&lt;0 or &gt;text.Length).
         /// </exception>
@@ -87,7 +87,7 @@ namespace System
         /// <param name="text">The target string.</param>
         /// <param name="start">The index at which to begin this slice.</param>
         /// <param name="length">The desired length for the slice (exclusive).</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is a null reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> index or <paramref name="length"/> is not in range.
         /// </exception>
diff --git a/src/System.Memory/src/System/MemoryExtensions.Portable.cs b/src/System.Memory/src/System/MemoryExtensions.Portable.cs
index 6b64749797..8e306acf6e 100644
--- a/src/System.Memory/src/System/MemoryExtensions.Portable.cs
+++ b/src/System.Memory/src/System/MemoryExtensions.Portable.cs
@@ -60,12 +60,12 @@ namespace System
         /// Creates a new readonly span over the portion of the target string.
         /// </summary>
         /// <param name="text">The target string.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is null.</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static ReadOnlySpan<char> AsReadOnlySpan(this string text)
         {
             if (text == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.text);
+                return default;
 
             return new ReadOnlySpan<char>(Unsafe.As<Pinnable<char>>(text), StringAdjustment, text.Length);
         }
@@ -75,7 +75,7 @@ namespace System
         /// </summary>
         /// <param name="text">The target string.</param>
         /// <param name="start">The index at which to begin this slice.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is null.</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> index is not in range (&lt;0 or &gt;text.Length).
         /// </exception>
@@ -83,7 +83,11 @@ namespace System
         public static ReadOnlySpan<char> AsReadOnlySpan(this string text, int start)
         {
             if (text == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.text);
+            {
+                if (start != 0)
+                    ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
+                return default;
+            }
             if ((uint)start > (uint)text.Length)
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
 
@@ -96,7 +100,7 @@ namespace System
         /// <param name="text">The target string.</param>
         /// <param name="start">The index at which to begin this slice.</param>
         /// <param name="length">The desired length for the slice (exclusive).</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is null.</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> index or <paramref name="length"/> is not in range.
         /// </exception>
@@ -104,7 +108,11 @@ namespace System
         public static ReadOnlySpan<char> AsReadOnlySpan(this string text, int start, int length)
         {
             if (text == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.text);
+            {
+                if (start != 0 || length != 0)
+                    ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
+                return default;
+            }
             if ((uint)start > (uint)text.Length || (uint)length > (uint)(text.Length - start))
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
 
@@ -113,11 +121,11 @@ namespace System
 
         /// <summary>Creates a new <see cref="ReadOnlyMemory{T}"/> over the portion of the target string.</summary>
         /// <param name="text">The target string.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is a null reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         public static ReadOnlyMemory<char> AsReadOnlyMemory(this string text)
         {
             if (text == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.text);
+                return default;
 
             return new ReadOnlyMemory<char>(text, 0, text.Length);
         }
@@ -125,14 +133,18 @@ namespace System
         /// <summary>Creates a new <see cref="ReadOnlyMemory{T}"/> over the portion of the target string.</summary>
         /// <param name="text">The target string.</param>
         /// <param name="start">The index at which to begin this slice.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is a null reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> index is not in range (&lt;0 or &gt;text.Length).
         /// </exception>
         public static ReadOnlyMemory<char> AsReadOnlyMemory(this string text, int start)
         {
             if (text == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.text);
+            {
+                if (start != 0)
+                    ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
+                return default;
+            }
             if ((uint)start > (uint)text.Length)
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
 
@@ -143,14 +155,18 @@ namespace System
         /// <param name="text">The target string.</param>
         /// <param name="start">The index at which to begin this slice.</param>
         /// <param name="length">The desired length for the slice (exclusive).</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="text"/> is a null reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="text"/> is null.</remarks>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> index or <paramref name="length"/> is not in range.
         /// </exception>
         public static ReadOnlyMemory<char> AsReadOnlyMemory(this string text, int start, int length)
         {
             if (text == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.text);
+            {
+                if (start != 0 || length != 0)
+                    ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
+                return default;
+            }
             if ((uint)start > (uint)text.Length || (uint)length > (uint)(text.Length - start))
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
 
diff --git a/src/System.Memory/src/System/ReadOnlySpan.Portable.cs b/src/System.Memory/src/System/ReadOnlySpan.Portable.cs
index a1025f3582..2d733fc35c 100644
--- a/src/System.Memory/src/System/ReadOnlySpan.Portable.cs
+++ b/src/System.Memory/src/System/ReadOnlySpan.Portable.cs
@@ -23,14 +23,16 @@ namespace System
         /// Creates a new read-only span over the entirety of the target array.
         /// </summary>
         /// <param name="array">The target array.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="array"/> is a null
-        /// reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
         /// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public ReadOnlySpan(T[] array)
         {
             if (array == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
+            {
+                this = default;
+                return; // returns default
+            }
 
             _length = array.Length;
             _pinnable = Unsafe.As<Pinnable<T>>(array);
@@ -44,8 +46,7 @@ namespace System
         /// <param name="array">The target array.</param>
         /// <param name="start">The index at which to begin the read-only span.</param>
         /// <param name="length">The number of items in the read-only span.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="array"/> is a null
-        /// reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
         /// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> or end index is not in the range (&lt;0 or &gt;=Length).
@@ -54,7 +55,12 @@ namespace System
         public ReadOnlySpan(T[] array, int start, int length)
         {
             if (array == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
+            {
+                if (start != 0 || length != 0)
+                    ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
+                this = default;
+                return; // returns default
+            }
             if ((uint)start > (uint)array.Length || (uint)length > (uint)(array.Length - start))
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
 
diff --git a/src/System.Memory/src/System/Span.Portable.cs b/src/System.Memory/src/System/Span.Portable.cs
index 39162b07a1..ba42e7e77a 100644
--- a/src/System.Memory/src/System/Span.Portable.cs
+++ b/src/System.Memory/src/System/Span.Portable.cs
@@ -23,14 +23,16 @@ namespace System
         /// Creates a new span over the entirety of the target array.
         /// </summary>
         /// <param name="array">The target array.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="array"/> is a null
-        /// reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
         /// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public Span(T[] array)
         {
             if (array == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
+            {
+                this = default;
+                return; // returns default
+            }
             if (default(T) == null && array.GetType() != typeof(T[]))
                 ThrowHelper.ThrowArrayTypeMismatchException();
 
@@ -46,8 +48,7 @@ namespace System
         /// <param name="array">The target array.</param>
         /// <param name="start">The index at which to begin the span.</param>
         /// <param name="length">The number of items in the span.</param>
-        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="array"/> is a null
-        /// reference (Nothing in Visual Basic).</exception>
+        /// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
         /// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
         /// <exception cref="System.ArgumentOutOfRangeException">
         /// Thrown when the specified <paramref name="start"/> or end index is not in the range (&lt;0 or &gt;=Length).
@@ -56,7 +57,12 @@ namespace System
         public Span(T[] array, int start, int length)
         {
             if (array == null)
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
+            {
+                if (start != 0 || length != 0)
+                    ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
+                this = default;
+                return; // returns default
+            }
             if (default(T) == null && array.GetType() != typeof(T[]))
                 ThrowHelper.ThrowArrayTypeMismatchException();
             if ((uint)start > (uint)array.Length || (uint)length > (uint)(array.Length - start))
diff --git a/src/System.Memory/src/System/ThrowHelper.cs b/src/System.Memory/src/System/ThrowHelper.cs
index 459b436f5b..4ba7eec5fd 100644
--- a/src/System.Memory/src/System/ThrowHelper.cs
+++ b/src/System.Memory/src/System/ThrowHelper.cs
@@ -106,17 +106,16 @@ namespace System
         }
     }
 
+    //
+    // The convention for this enum is using the argument name as the enum name
+    //
     internal enum ExceptionArgument
     {
         array,
         length,
         start,
-        text,
-        obj,
-        ownedMemory,
         minimumBufferSize,
         byteOffset,
-        pointer,
         comparable,
         comparer
     }
diff --git a/src/System.Memory/tests/Memory/CtorArray.cs b/src/System.Memory/tests/Memory/CtorArray.cs
index d5b153768f..e2f67d1162 100644
--- a/src/System.Memory/tests/Memory/CtorArray.cs
+++ b/src/System.Memory/tests/Memory/CtorArray.cs
@@ -71,8 +71,13 @@ namespace System.MemoryTests
         [Fact]
         public static void CtorArrayNullArray()
         {
-            Assert.Throws<ArgumentNullException>(() => new Memory<int>(null));
-            Assert.Throws<ArgumentNullException>(() => new Memory<int>(null, 0, 0));
+            var memory = new Memory<int>(null);
+            memory.Validate();
+            Assert.Equal(default, memory);
+
+            memory = new Memory<int>(null, 0, 0);
+            memory.Validate();
+            Assert.Equal(default, memory);
         }
 
         [Fact]
diff --git a/src/System.Memory/tests/ReadOnlyMemory/CtorArray.cs b/src/System.Memory/tests/ReadOnlyMemory/CtorArray.cs
index 046398c076..f4ddfe7daa 100644
--- a/src/System.Memory/tests/ReadOnlyMemory/CtorArray.cs
+++ b/src/System.Memory/tests/ReadOnlyMemory/CtorArray.cs
@@ -72,8 +72,13 @@ namespace System.MemoryTests
         [Fact]
         public static void CtorArrayNullArray()
         {
-            Assert.Throws<ArgumentNullException>(() => new ReadOnlyMemory<int>(null));
-            Assert.Throws<ArgumentNullException>(() => new ReadOnlyMemory<int>(null, 0, 0));
+            var memory = new ReadOnlyMemory<int>(null);
+            memory.Validate();
+            Assert.Equal(default, memory);
+
+            memory = new ReadOnlyMemory<int>(null, 0, 0);
+            memory.Validate();
+            Assert.Equal(default, memory);
         }
 
         [Fact]
diff --git a/src/System.Memory/tests/ReadOnlyMemory/Strings.cs b/src/System.Memory/tests/ReadOnlyMemory/Strings.cs
index 592f398987..248cf818c3 100644
--- a/src/System.Memory/tests/ReadOnlyMemory/Strings.cs
+++ b/src/System.Memory/tests/ReadOnlyMemory/Strings.cs
@@ -54,11 +54,19 @@ namespace System.MemoryTests
         }
 
         [Fact]
-        public static void AsReadOnlyMemory_NullString_Throws()
+        public static void AsReadOnlyMemory_NullString_Default()
         {
-            AssertExtensions.Throws<ArgumentNullException>("text", () => ((string)null).AsReadOnlyMemory());
-            AssertExtensions.Throws<ArgumentNullException>("text", () => ((string)null).AsReadOnlyMemory(0));
-            AssertExtensions.Throws<ArgumentNullException>("text", () => ((string)null).AsReadOnlyMemory(0, 0));
+            ReadOnlyMemory<char> m = ((string)null).AsReadOnlyMemory();
+            m.Validate();
+            Assert.Equal(default, m);
+
+            m = ((string)null).AsReadOnlyMemory(0);
+            m.Validate();
+            Assert.Equal(default, m);
+
+            m = ((string)null).AsReadOnlyMemory(0, 0);
+            m.Validate();
+            Assert.Equal(default, m);
         }
 
         [Fact]
@@ -191,14 +199,14 @@ namespace System.MemoryTests
         [MemberData(nameof(TestHelpers.StringSlice2ArgTestOutOfRangeData), MemberType = typeof(TestHelpers))]
         public static unsafe void AsReadOnlyMemory_2Arg_OutOfRange(string text, int start)
         {
-            AssertExtensions.Throws<ArgumentOutOfRangeException>("start", () => text.AsReadOnlyMemory(start));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("Start", () => text.AsReadOnlyMemory(start));
         }
 
         [Theory]
         [MemberData(nameof(TestHelpers.StringSlice3ArgTestOutOfRangeData), MemberType = typeof(TestHelpers))]
         public static unsafe void AsReadOnlyMemory_3Arg_OutOfRange(string text, int start, int length)
         {
-            AssertExtensions.Throws<ArgumentOutOfRangeException>("start", () => text.AsReadOnlyMemory(start, length));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("Start", () => text.AsReadOnlyMemory(start, length));
         }
 
         [Fact]
diff --git a/src/System.Memory/tests/ReadOnlySpan/AsReadOnlySpan.cs b/src/System.Memory/tests/ReadOnlySpan/AsReadOnlySpan.cs
index 71dfa9b417..dc69d4a086 100644
--- a/src/System.Memory/tests/ReadOnlySpan/AsReadOnlySpan.cs
+++ b/src/System.Memory/tests/ReadOnlySpan/AsReadOnlySpan.cs
@@ -40,7 +40,9 @@ namespace System.SpanTests
         public static void NullArrayAsReadOnlySpan()
         {
             int[] a = null;
-            Assert.Throws<ArgumentNullException>(() => a.AsReadOnlySpan().DontBox());
+            ReadOnlySpan<int> span = a.AsReadOnlySpan();
+            span.Validate();
+            Assert.True(span == default);
         }
 
         [Fact]
@@ -117,9 +119,17 @@ namespace System.SpanTests
         public static void StringAsReadOnlySpanNullChecked()
         {
             string s = null;
-            Assert.Throws<ArgumentNullException>(() => s.AsReadOnlySpan().DontBox());
-            Assert.Throws<ArgumentNullException>(() => s.AsReadOnlySpan(0).DontBox());
-            Assert.Throws<ArgumentNullException>(() => s.AsReadOnlySpan(0, 0).DontBox());
+            ReadOnlySpan<char> span = s.AsReadOnlySpan();
+            span.Validate();
+            Assert.True(span == default);
+
+            span = s.AsReadOnlySpan(0);
+            span.Validate();
+            Assert.True(span == default);
+
+            span = s.AsReadOnlySpan(0, 0);
+            span.Validate();
+            Assert.True(span == default);
         }
 
         [Fact]
@@ -174,14 +184,14 @@ namespace System.SpanTests
         [MemberData(nameof(TestHelpers.StringSlice2ArgTestOutOfRangeData), MemberType = typeof(TestHelpers))]
         public static unsafe void AsReadOnlySpan_2Arg_OutOfRange(string text, int start)
         {
-            AssertExtensions.Throws<ArgumentOutOfRangeException>("start", () => text.AsReadOnlySpan(start).DontBox());
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("Start", () => text.AsReadOnlySpan(start).DontBox());
         }
 
         [Theory]
         [MemberData(nameof(TestHelpers.StringSlice3ArgTestOutOfRangeData), MemberType = typeof(TestHelpers))]
         public static unsafe void AsReadOnlySpan_3Arg_OutOfRange(string text, int start, int length)
         {
-            AssertExtensions.Throws<ArgumentOutOfRangeException>("start", () => text.AsReadOnlySpan(start, length).DontBox());
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("Start", () => text.AsReadOnlySpan(start, length).DontBox());
         }
     }
 }
diff --git a/src/System.Memory/tests/ReadOnlySpan/CtorArray.cs b/src/System.Memory/tests/ReadOnlySpan/CtorArray.cs
index ea8f3ba831..f72a3c6dbb 100644
--- a/src/System.Memory/tests/ReadOnlySpan/CtorArray.cs
+++ b/src/System.Memory/tests/ReadOnlySpan/CtorArray.cs
@@ -72,8 +72,13 @@ namespace System.SpanTests
         [Fact]
         public static void CtorArrayNullArray()
         {
-            Assert.Throws<ArgumentNullException>(() => new ReadOnlySpan<int>(null).DontBox());
-            Assert.Throws<ArgumentNullException>(() => new ReadOnlySpan<int>(null, 0, 0).DontBox());
+            var span = new ReadOnlySpan<int>(null);
+            span.Validate();
+            Assert.True(span == default);
+
+            span = new ReadOnlySpan<int>(null, 0, 0);
+            span.Validate();
+            Assert.True(span == default);
         }
 
         [Fact]
diff --git a/src/System.Memory/tests/Span/CtorArray.cs b/src/System.Memory/tests/Span/CtorArray.cs
index 6105a99748..a26334a009 100644
--- a/src/System.Memory/tests/Span/CtorArray.cs
+++ b/src/System.Memory/tests/Span/CtorArray.cs
@@ -71,8 +71,13 @@ namespace System.SpanTests
         [Fact]
         public static void CtorArrayNullArray()
         {
-            Assert.Throws<ArgumentNullException>(() => new Span<int>(null).DontBox());
-            Assert.Throws<ArgumentNullException>(() => new Span<int>(null, 0, 0).DontBox());
+            var span = new Span<int>(null);
+            span.Validate();
+            Assert.True(span == default);
+
+            span = new Span<int>(null, 0, 0);
+            span.Validate();
+            Assert.True(span == default);
         }
 
         [Fact]