Submission isn't set on __init__ thus we need to update it.

def _update_submission(self, submission):
        """Submission isn't set on __init__ thus we need to update it."""
        submission._comments_by_id[self.name] = self  # pylint: disable=W0212
        self._submission = submission
        if self._replies:
            for reply in self._replies:
                reply._update_submission(submission)