Don't throw when navigating to non-blob

Author: jcansdale

src/GitHub.App/Services/GitHubContextService.cs

@@ -308,12 +308,19 @@ public string ResolvePath(GitHubContext context)
 
             using (var repository = gitService.GetRepository(repositoryDir))
             {
-                var objectishPath = context.TreeishPath;
-                if (context.BlobName != null)
+                if (context.TreeishPath == null)
                 {
-                    objectishPath += '/' + context.BlobName;
+                    // Blobs without a TreeishPath aren't currently supported
+                    return (null, null);
                 }
 
+                if (context.BlobName == null)
+                {
+                    // Not a blob
+                    return (null, null);
+                }
+
+                var objectishPath = $"{context.TreeishPath}/{context.BlobName}";
                 foreach (var objectish in ToObjectish(objectishPath))
                 {
                     var commit = repository.Lookup(objectish.commitish);

test/GitHub.App.UnitTests/Services/GitHubContextServiceTests.cs

@@ -330,7 +330,8 @@ public class TheResolveGitObjectMethod
         [TestCase("https://github.com/github/VisualStudio/blob/branch-name/src/foo.cs", "branch-name", "branch-name:src/foo.cs", "branch-name", "src/foo.cs")]
         [TestCase("https://github.com/github/VisualStudio/blob/fixes/666-bug/src/foo.cs", "fixes/666-bug", "fixes/666-bug:src/foo.cs", "fixes/666-bug", "src/foo.cs")]
         [TestCase("https://github.com/github/VisualStudio/blob/fixes/666-bug/A/B/foo.cs", "fixes/666-bug", "fixes/666-bug:A/B/foo.cs", "fixes/666-bug", "A/B/foo.cs")]
-        [TestCase("https://github.com/github/VisualStudio/blob/master/foo.cs", "master", "", "master", null, Description = "Resolve commit only")]
+        [TestCase("https://github.com/github/VisualStudio/blob/master/foo.cs", "master", null, "master", null, Description = "Resolve commit only")]
+        [TestCase("https://github.com/github/VisualStudio/commit/8cf9a268c497adb4fc0a14572253165e179dd11e", "8cf9a268c497adb4fc0a14572253165e179dd11e", null, null, null)]
         public void ResolveGitObject(string url, string commitish, string objectish, string expectCommitish, string expectPath)
         {
             var repositoryDir = "repositoryDir";