为响应中的特定槽位提供槽位值并恢复对话

"use strict";

const lexResponses = require("./lexResponse");

const depart = ["one-way", "oneway"];

const buildValidationResult = (isValid, violatedSlot, messageContent) => {
  if (messageContent == null) {
    return {
      isValid: isValid,
      violatedSlot: violatedSlot,
    };
  }
  return {
    isValid: isValid,
    violatedSlot: violatedSlot,
    message: { contentType: "PlainText", content: messageContent },
  };
};

function validateBookaflight(
  Departing,
  ReturnDate
) {
  if (Departing && depart.indexOf(Departing.toLowerCase()) === -1) {
   
     return {
          dialogAction: {
            type: "ElicitSlot",
            intentName: "Bookaflight",
            slots: {
              Departure_city: Departure_city,
              Arrival_city: Arrival_city,
              Departing: Departing,
              ReturnDate: ReturnDate,
            },
            slotToElicit: "ReturnDate",
            message: {
              contentType: "PlainText",
              content: "Please enter return date,(yyyy-mm-dd)",
            },
          },
        }
    };
     return buildValidationResult(true, null, null);
}

function buildFulfilmentResult(fullfilmentState, messageContent) {
  return {
    fullfilmentState,
    message: { contentType: "PlainText", content: messageContent },
  };
}

An error has occurred: Invalid Lambda 
Response: Received invalid response from 
Lambda: Can not construct instance of 
ElicitSlotDialogAction, problem: 
slotToElicit must not be blank in ElicitSlot 
dialog action at 
[Source: {"sessionAttributes":{},"dialogAction":{"type":"ElicitSlot","intentName":"Bookaflight",
"slots":{"ReturnDate":null,"Departure_city":"london","Flight_schedule":null,"Arrival_city":"lahore","Date":null,
"Departing":"roundtrip",
"undefined":null}}}; line: 1, column: 241]