适用于社交提供商的FirebaseAuth事件的云功能

创建用户时尝试更新实时数据库中的用户数据.这是我的代码:

const functiOns= require('firebase-functions');
const promise = require('request-promise');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

var omitBy = require('lodash.omitby');
var isNil = require('lodash.isnil');

'use strict';

exports.userCreated = functions.auth.user().onCreate(event => {

  let request = admin.auth().getUser(event.data.uid)
  .then(function(user) {
    console.log("Successfully fetched user data: ", user.toJSON());

    var email, firstName, lastName, photoURL;

    for (var provider of user.providerData) {

      if (provider.email) {
        email = provider.email;
      }

      if (provider.photoURL) {
        photoURL = provider.photoURL;
      }

      if (provider.displayName) {
        const names = provider.displayName.split(' ');
        firstName = names[0];

        if (names.length > 1) {
          lastName = names[names.length - 1];
        }
      }
    }

    var values = omitBy({
      email: email,
      first_name: firstName,
      last_name: lastName,
      license_agreement_version: '1.1',
      image_url: photoURL
    }, isNil);

    admin.database().ref('users/' + user.uid).set(values);
  })
  .catch(function(error) {
    console.error("Error Fetching User: ", error);
  });

  return request;
});

但是,当通过创建用户时.Facebook,未提供提供商数据.这是控制台日志:

Successfully fetched user data: { uid: 'exampleUID',
  email: undefined,
  emailVerified: false,
  displayName: undefined,
  photoURL: undefined,
  disabled: false,
  metadata: 
   { lastSignedInAt: 2017-03-16T19:40:59.000Z,
     createdAt: 2017-03-16T19:40:59.000Z },
  providerData: [] }

我做错了什么,或者这些数据是否会在创作时提供？