Add null check to TagCollection

Author: asbjornu

src/GitVersion.LibGit2Sharp/Git/TagCollection.cs

@@ -1,11 +1,16 @@
+using GitVersion.Extensions;
+
 namespace GitVersion;
 
 internal sealed class TagCollection : ITagCollection
 {
     private readonly LibGit2Sharp.TagCollection innerCollection;
-    internal TagCollection(LibGit2Sharp.TagCollection collection) => this.innerCollection = collection;
 
-    public IEnumerator<ITag> GetEnumerator() => this.innerCollection.Select(tag => new Tag(tag)).GetEnumerator();
+    internal TagCollection(LibGit2Sharp.TagCollection collection)
+        => this.innerCollection = collection.NotNull();
+
+    public IEnumerator<ITag> GetEnumerator()
+        => this.innerCollection.Select(tag => new Tag(tag)).GetEnumerator();
 
     IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
 }