Add null checks to Reference

Author: asbjornu

src/GitVersion.LibGit2Sharp/Git/Reference.cs

@@ -1,3 +1,4 @@
+using GitVersion.Extensions;
 using GitVersion.Helpers;
 using LibGit2Sharp;
 
@@ -7,25 +8,26 @@ internal sealed class Reference : IReference
     {
         private static readonly LambdaEqualityHelper<IReference> equalityHelper = new(x => x.Name.Canonical);
         private static readonly LambdaKeyComparer<IReference, string> comparerHelper = new(x => x.Name.Canonical);
-
         internal readonly LibGit2Sharp.Reference innerReference;
 
         internal Reference(LibGit2Sharp.Reference reference)
         {
-            this.innerReference = reference;
+            this.innerReference = reference.NotNull();
             Name = new ReferenceName(reference.CanonicalName);
 
             if (reference is DirectReference)
                 ReferenceTargetId = new ObjectId(reference.TargetIdentifier);
         }
+
         public ReferenceName Name { get; }
         public IObjectId? ReferenceTargetId { get; }
         public int CompareTo(IReference other) => comparerHelper.Compare(this, other);
-        public override bool Equals(object obj) => Equals((obj as IReference));
+        public override bool Equals(object obj) => Equals(obj as IReference);
         public bool Equals(IReference? other) => equalityHelper.Equals(this, other);
         public override int GetHashCode() => equalityHelper.GetHashCode(this);
         public override string ToString() => Name.ToString();
         public string TargetIdentifier => this.innerReference.TargetIdentifier;
-        public static implicit operator LibGit2Sharp.Reference(Reference d) => d.innerReference;
+        public static implicit operator LibGit2Sharp.Reference(Reference d)
+            => d.NotNull().innerReference;
     }
 }