Steps to reproduce:
- Open a diff.
- Write an inline comment
- Delete the inline comment
- Start writing another inline comment
- (Optionally) Cancel writing the second inline comment
- Click on "Changes discarded. Undo"
Popup says
```Argument 2 passed to DifferentialInlineCommentEditController::canEditInlineComment() must be an instance of DifferentialInlineComment, boolean given, called in /core/lib/phabricator/src/applications/differential/controller/DifferentialInlineCommentEditController.php on line 63 and defined```