code: function (evt, aggregateModel) {
      if (!this.evtFn) {
        return;
      }
  
      if (!this.payload || this.payload === '') {
        this.evtFn(evt, aggregateModel);
        return;
      }
  
      var payload = dotty.get(evt, this.payload);
      this.evtFn(payload, aggregateModel);
    }
docs: Apply an event.
  @param {Object}         evt            The event object.
  @param {AggregateModel} aggregateModel The aggregate object.