Port some tests from cgit and fix implementation to make them pass

1 files changed, 8 insertions, 1 deletions

diff --git a/LibGit2Sharp/TagCollection.cs b/LibGit2Sharp/TagCollection.cs
index 17031e56..941bf5d7 100644
--- a/LibGit2Sharp/TagCollection.cs
+++ b/LibGit2Sharp/TagCollection.cs
@@ -120,7 +120,14 @@ namespace LibGit2Sharp
         {
             Ensure.ArgumentNotNullOrEmptyString(name, "name");
 
-            repo.Refs.Delete(this[name].CanonicalName);  //TODO: To be replaced by native libgit2 git_tag_delete() when available.
+            Tag tag = this[name];
+
+            if (tag == null)
+            {
+                throw new ApplicationException(String.Format("No tag identified by '{0}' can be found in the repository.", name));
+            }
+
+            repo.Refs.Delete(tag.CanonicalName);  //TODO: To be replaced by native libgit2 git_tag_delete() when available.
         }
 
         private GitObject RetrieveObjectToTag(string target)