Add null checks to GitObject and ObjectId

Author: asbjornu

src/GitVersion.LibGit2Sharp/Git/GitObject.cs

@@ -9,6 +9,9 @@ internal class GitObject : IGitObject
 
     internal GitObject(LibGit2Sharp.GitObject innerGitObject)
     {
+        if (innerGitObject == null)
+            throw new ArgumentNullException(nameof(innerGitObject));
+        
         Id = new ObjectId(innerGitObject.Id);
         Sha = innerGitObject.Sha;
     }

src/GitVersion.LibGit2Sharp/Git/ObjectId.cs

@@ -8,7 +8,9 @@ internal sealed class ObjectId : IObjectId
     private static readonly LambdaKeyComparer<IObjectId, string> comparerHelper = new(x => x.Sha);
 
     private readonly LibGit2Sharp.ObjectId innerObjectId;
-    internal ObjectId(LibGit2Sharp.ObjectId objectId) => this.innerObjectId = objectId;
+
+    internal ObjectId(LibGit2Sharp.ObjectId objectId) =>
+        this.innerObjectId = objectId ?? throw new ArgumentNullException(nameof(objectId));
 
     public ObjectId(string sha) : this(new LibGit2Sharp.ObjectId(sha))
     {