code: function (parameters, callback) {
          callback(util.format('Sorry, there are no %s rooms available at %s for your chosen dates (%s) to (%s), please try another search.',
              parameters.RoomType || '', parameters.Place, formatDate(parameters.Checkin), formatDate(parameters.Checkout)));
      }
docs: Action fulfillment method, recieves parameters as keyed-object (parameters argument) and a callback function to invoke with the fulfillment result.