PullRequest.Head can be null.

Author: grokys

src/GitHub.App/Models/PullRequestModel.cs

@@ -154,6 +154,7 @@ public string Body
         }
 
         public GitReferenceModel Base { get; set; }
+        [AllowNull]
         public GitReferenceModel Head { get; set; }
         public DateTimeOffset CreatedAt { get; set; }
         public DateTimeOffset UpdatedAt { get; set; }

src/GitHub.App/Services/ModelService.cs

@@ -370,7 +370,7 @@ IPullRequestModel Create(PullRequestCacheItem prCacheItem)
                 CommentCount = prCacheItem.CommentCount,
                 CommitCount = prCacheItem.CommitCount,
                 CreatedAt = prCacheItem.CreatedAt,
-                Head = prCacheItem.Head ?? new GitReferenceModel(),
+                Head = prCacheItem.Head,
                 State = prCacheItem.State.HasValue ? 
                     prCacheItem.State.Value : 
                     prCacheItem.IsOpen.Value ? PullRequestStateEnum.Open : PullRequestStateEnum.Closed,                
@@ -476,7 +476,9 @@ public PullRequestCacheItem(PullRequest pr, IReadOnlyList<PullRequestFile> files
                 Title = pr.Title;
                 Number = pr.Number;
                 Base = new GitReferenceModel { Label = pr.Base.Label, Ref = pr.Base.Ref, RepositoryCloneUrl = pr.Base.Repository.CloneUrl };
-                Head = new GitReferenceModel { Label = pr.Head.Label, Ref = pr.Head.Ref, RepositoryCloneUrl = pr.Head.Repository.CloneUrl };
+                Head = pr.Head != null ?
+                    new GitReferenceModel { Label = pr.Head.Label, Ref = pr.Head.Ref, RepositoryCloneUrl = pr.Head.Repository.CloneUrl } :
+                    null;
                 CommentCount = pr.Comments + pr.ReviewComments;
                 CommitCount = pr.Commits;
                 Author = new AccountCacheItem(pr.User);

src/GitHub.App/ViewModels/PullRequestDetailViewModel.cs

@@ -254,7 +254,7 @@ public override void Initialize([AllowNull] ViewWithData data)
         public async Task Load(IPullRequestModel pullRequest)
         {
             Model = pullRequest;
-            SourceBranchDisplayName = GetBranchDisplayName(pullRequest.Head.Label);
+            SourceBranchDisplayName = GetBranchDisplayName(pullRequest.Head?.Label);
             TargetBranchDisplayName = GetBranchDisplayName(pullRequest.Base.Label);
             Body = !string.IsNullOrWhiteSpace(pullRequest.Body) ? pullRequest.Body : "*No description provided.*";
 
@@ -376,9 +376,16 @@ static PullRequestDirectoryNode GetDirectory(string path, Dictionary<string, Pul
 
         string GetBranchDisplayName(string targetBranchLabel)
         {
-            var parts = targetBranchLabel.Split(':');
-            var owner = parts[0];
-            return owner == repository.CloneUrl.Owner ? parts[1] : targetBranchLabel;
+            if (targetBranchLabel != null)
+            {
+                var parts = targetBranchLabel.Split(':');
+                var owner = parts[0];
+                return owner == repository.CloneUrl.Owner ? parts[1] : targetBranchLabel;
+            }
+            else
+            {
+                return "[Invalid]";
+            }
         }
 
         IObservable<Unit> DoCheckout(object unused)

src/UnitTests/GitHub.App/ViewModels/PullRequestDetailViewModelTests.cs

@@ -285,6 +285,20 @@ public async Task CheckoutInvalidStateShouldCallService()
             unused = target.Item2.Received().FetchAndCheckout(Arg.Any<ILocalRepositoryModel>(), target.Item1.Model.Number, "pr/1-foo");
         }
 
+        [Fact]
+        public async Task ShouldAcceptNullHead()
+        {
+            var target = CreateTarget();
+            var model = CreatePullRequest();
+
+            // PullRequest.Head can be null for example if a user deletes the repository after creating the PR.
+            model.Head = null;
+
+            await target.Load(model);
+
+            Assert.Equal("[Invalid]", target.SourceBranchDisplayName);
+        }
+
         PullRequestDetailViewModel CreateTarget(
             string currentBranch = "master",
             string existingPrBranch = null,