code: private SnsMessage.Builder<? extends SnsMessage.Builder> unmarshallNotification(SnsJsonNode message) {
          return SnsNotification.builder(client)
                                .withMessage(message.getString(MESSAGE))
                                .withSubject(message.getString(SUBJECT))
                                .withUnsubscribeUrl(message.getString(UNSUBSCRIBE_URL));
      }
docs: Unmarshall into a {@link SnsNotification} object.
  
  @param message JSON message.
  @return Builder with sub properties filled in. Base properties are added by
  {@link #unmarshallBase(SnsMessage.Builder, SnsJsonNode)}.