code: function (aggId, cmd, clb) {
      if (!aggId || !_.isString(aggId)) {
        var err = new Error('Please pass a valid aggregate id!');
        debug(err);
        throw err;
      }
      if (!cmd || !_.isObject(cmd)) {
        var err = new Error('Please pass a valid command!');
        debug(err);
        throw err;
      }
      if (!clb || !_.isFunction(clb)) {
        var err = new Error('Please pass a valid callback!');
        debug(err);
        throw err;
      }
  
      this.queue[aggId] = this.queue[aggId] || [];
      this.queue[aggId].push({ command: cmd, callback: clb })
    }
docs: Queues the passed command and its callback.
  @param {String}   aggId The passed aggregate id.
  @param {Object}   cmd   The command to be queued.
  @param {Function} clb   The callback of this command.