code: function (evt, callback) {
      var self = this;
      var callbacked = false;
  
      function handleError (err) {
        debug(err);
        callbacked = true;
        callback(err);
      }
  
      try {
        if (this.transformFn.length === 2) {
          this.transformFn(_.cloneDeep(evt), function (err, newEvt) {
            if (err) return handleError(err);
            callbacked = true;
            callback(null, newEvt);
          });
        } else {
          var newEvt = this.transformFn(_.cloneDeep(evt));
          callback(null, newEvt);
        }
      } catch (err) {
        if (!callbacked) {
          return handleError(err);
        }
        throw err;
      }
    }
docs: transform an CommittingEventTransformer.
  @param {Object}   evt      The CommittingEventTransformer object.
  @param {Function} callback The function, that will be called when this action is completed.
  `function(err, evt){}`