Firebase 消息应用程序的推送通知

Question

var admin = require("firebase-admin");
var functions=require("firebase-functions");
var serviceAccount = require("./chap-fapp-d3179-firebase-adminsdk-vgm2q-0c32f02f66.json");
admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  databaseURL: "https://chap-fapp-d3179-default-rtdb.firebaseio.com"
});
exports.sentNotification=functions.database.ref('/Notifications/{receiver_user_id}/{notification_id}')
.onWrite((data,context)=>{
    const receiver_user_id=context.params.receiver_user_id;
    const notification_id=context.params.notification_id;
    console.log('We have a notification to send to :',receiver_user_id);
    if(!data.after.val())
    {
        console.log('A notification has been deleted :',notification_id);
        return null;
    }
    const DeviceToken=admin.database().ref('/Users/{receiver_user_id}/device_token').once('value');
    return DeviceToken.then(result =>
    {
        const token_id=result.val();
        const payload=
        {
            notification:{
                title: "New Chat Request",
                body: '{senderUserName} want to connect with you',
                icon: "default"
            
            }
        };
        return admin.messaging().sendToDevice(token_id,payload)
        .then(response=>{
            console.log('This was a notification feature..');
        });
    });

        
    });

错误：

错误：提供给 sendToDevice() 的注册令牌必须是非空字符串或非空数组。 在 FirebaseMessagingError.FirebaseError [作为构造函数] (/workspace/node_modules/firebase-admin/lib/utils/error.js:44:28) 在 FirebaseMessagingError.PrefixedFirebaseError [作为构造函数] (/workspace/node_modules/firebase-admin/lib/ utils/error.js:90:28) 在新的 FirebaseMessagingError (/workspace/node_modules/firebase-admin/lib/utils/error.js:279:16) 在 Messaging.validateRegistrationTokensType (/workspace/node_modules/firebase-admin/lib /messaging/messaging.js:774:19) 在 Messaging.sendToDevice (/workspace/node_modules/firebase-admin/lib/messaging/messaging.js:344:14) 在 /workspace/index.js:32:28 在 processTicksAndRejections （节点：内部/进程/task_queues：96：5）