无法从Firebase的数据库读取值

Question

尝试使用两个uid检索与示例项目相似的两个用户，并从一个中获取fullName值，并从另一个中获取fcmToken值。数据库的结构是/ users / {uid} / fcmToken和/ users / {uid} / fullName。我收到未处理的异常，并且无法以空值读取fullName：

exports.sendFriendRequestPushNotification = functions.https.onRequest((req, res) => {

  // Grab the parameters
  const requestingUid = req.query.requestingUid; //User sending the request
  const requestedUid = req.query.requestedUid; //User receiving the request

  const getRequestingProfilePromise = admin.database()
  .ref(`/users/${requestingUid}`).once('value');

  const getRequestedProfilePromise = admin.database()
  .ref(`/users/${requestedUid}`).once('value');

  return Promise.all([getRequestingProfilePromise, getRequestedProfilePromise]).then(results => {
    const requestingName = results[0].val().fullName;
    const fcmToken = results[1].val().fcmToken;

    console.log('requestingName: ', requestingName, 'fcmToken: ', fcmToken);

    // Notification details.
    const payload = {
    notification: {
      title: 'Looks like you\'re popular',
      body: requestingName + ' wants to be friends!',
      notificationType: "friendRequest"
    },
    data : {
      notificationType : "friendRequest"
    }
  };

  // Send notification
  return admin.messaging().sendToDevice(fcmToken, payload);
  })
});