code: function (aggregate, cmd, callback) {
      if (!aggregate || !_.isObject(aggregate)) {
        var err = new Error('Please pass a valid aggregate!');
        debug(err);
        throw err;
      }
      if (!cmd || !_.isObject(cmd)) {
        var err = new Error('Please pass a valid command!');
        debug(err);
        throw err;
      }
      if (!callback || !_.isFunction(callback)) {
        var err = new Error('Please pass a valid function!');
        debug(err);
        throw err;
      }
  
      this.aggregate.handle(aggregate, cmd, callback);
    }
docs: Handles the command by passing it to the handle function of the aggregate.
  @param {AggregateModel} aggregate The passed aggregate.
  @param {Object}         cmd       The command.
  @param {Function}       callback  The function, that will be called when this action is completed.
  `function(err){}`