code: function(err, res) {
        console.log(err);
        var MSG_ERR = this.conf.CONST.MSG_ERR;
        if (_.isArray(MSG_ERR)) {
          res.reply(_.sample(MSG_ERR));
        } else {
          res.reply(MSG_ERR);
        }
        return;
      }
docs: /*
  Called when an error occurs. Respond plain text conf.CONST.MSG_ERR to
  client by default.
  
  Now rolling message is supported. conf.CONST.MSG_ERR could be an array,
  _err() will choose one of them randomly. Even an object which
  represents a reply-with-pic is allowed to be in the array.
  
  *err*, message of the error, will be logged.
  *res*, will call res.reply() to respond to client.