Add null check to RefSpec

Author: asbjornu

src/GitVersion.LibGit2Sharp/Git/RefSpec.cs

@@ -1,3 +1,4 @@
+using GitVersion.Extensions;
 using GitVersion.Helpers;
 
 namespace GitVersion;
@@ -6,17 +7,16 @@ public class RefSpec : IRefSpec
 {
     private static readonly LambdaEqualityHelper<IRefSpec> equalityHelper = new(x => x.Specification);
     private static readonly LambdaKeyComparer<IRefSpec, string> comparerHelper = new(x => x.Specification);
-
     private readonly LibGit2Sharp.RefSpec innerRefSpec;
 
-    internal RefSpec(LibGit2Sharp.RefSpec refSpec) => this.innerRefSpec = refSpec;
+    internal RefSpec(LibGit2Sharp.RefSpec refSpec) => this.innerRefSpec = refSpec.NotNull();
     public int CompareTo(IRefSpec other) => comparerHelper.Compare(this, other);
     public bool Equals(IRefSpec? other) => equalityHelper.Equals(this, other);
-    public override bool Equals(object obj) => Equals((obj as IRefSpec));
-    public override int GetHashCode() => equalityHelper.GetHashCode(this);
-    public override string ToString() => Specification;
     public string Specification => this.innerRefSpec.Specification;
     public RefSpecDirection Direction => (RefSpecDirection)this.innerRefSpec.Direction;
     public string Source => this.innerRefSpec.Source;
     public string Destination => this.innerRefSpec.Destination;
+    public override bool Equals(object obj) => Equals((obj as IRefSpec));
+    public override int GetHashCode() => equalityHelper.GetHashCode(this);
+    public override string ToString() => Specification;
 }