Fix error when viewing diffs without blobs41468-error-500-trying-to-view-a-merge-request-json-undefined-method-binary-for-nil-nilclass

Old merge requests can have diffs without corresponding blobs. (This also may be
possible for commit diffs in corrupt repositories.)

We can't use the `&.` operator on the blobs, because the blob objects are never
nil, but `BatchLoader` instances that delegate to `Blob`. We can't use
`Object#try`, because `Blob` doesn't inherit from `Object`.

`BatchLoader` provides a `__sync` method that returns the delegated object, but
using `itself` also works because it's forwarded, and will work for
non-`BatchLoader` instances too. So the simplest solution is to just use that
with the `&.` operator.

1 files changed, 25 insertions, 0 deletions

diff --git a/spec/lib/gitlab/diff/file_spec.rb b/spec/lib/gitlab/diff/file_spec.rb
index ff9acfd08b9..9204ea37963 100644
--- a/spec/lib/gitlab/diff/file_spec.rb
+++ b/spec/lib/gitlab/diff/file_spec.rb
@@ -431,4 +431,29 @@ describe Gitlab::Diff::File do
       end
     end
   end
+
+  context 'when neither blob exists' do
+    let(:blank_diff_refs) { Gitlab::Diff::DiffRefs.new(base_sha: Gitlab::Git::BLANK_SHA, head_sha: Gitlab::Git::BLANK_SHA) }
+    let(:diff_file) { described_class.new(diff, diff_refs: blank_diff_refs, repository: project.repository) }
+
+    describe '#blob' do
+      it 'returns a concrete nil so it can be used in boolean expressions' do
+        actual = diff_file.blob && true
+
+        expect(actual).to be_nil
+      end
+    end
+
+    describe '#binary?' do
+      it 'returns false' do
+        expect(diff_file).not_to be_binary
+      end
+    end
+
+    describe '#size' do
+      it 'returns zero' do
+        expect(diff_file.size).to be_zero
+      end
+    end
+  end
 end