def _MergeEventTag(self, storage_writer, attribute_container):
    if attribute_container.CONTAINER_TYPE != 'event_tag':
      return
    event_identifier = attribute_container.GetEventIdentifier()
    if not event_identifier:
      return
    stored_event_tag = self._event_tag_index.GetEventTagByIdentifier(
        storage_writer, event_identifier)
    if stored_event_tag:
      attribute_container.AddComment(stored_event_tag.comment)
      attribute_container.AddLabels(stored_event_tag.labels)
    self._event_tag_index.SetEventTag(attribute_container)