protected void maybeUnsubscribeChangeTopic() {
    if (notifier != null) {
      notifier.unsubscribe(ACCOUNT_METADATA_CHANGE_TOPIC, changeTopicListener);
      notifier.close();
    }
  }
Return the {@link Notifier}.
@return The {@link Notifier}
ambry-account/src/main/java/com/github/ambry/account/AbstractAccountService.java