code: private void doQueueIsEmpty(final Message<JsonObject> message) {
      final String name = message.body().getString("name");
      if (name == null) {
        message.reply(new JsonObject().putString("status", "error").putString("message", "No name specified."));
        return;
      }
  
      context.execute(new Action<Boolean>() {
        @Override
        public Boolean perform() {
          return data.getQueue(formatKey(name)).isEmpty();
        }
      }, new Handler<AsyncResult<Boolean>>() {
        @Override
        public void handle(AsyncResult<Boolean> result) {
          if (result.failed()) {
            message.reply(new JsonObject().putString("status", "error").putString("message", result.cause().getMessage()));
          } else {
            message.reply(new JsonObject().putString("status", "ok").putBoolean("result", result.result()));
          }
        }
      });
    }
docs: Handles cluster queue is empty command.