Firebase Error: Registration token(s) provided to sendToDevice() must be a non-empty string or a non-empty...
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i want to send users notification when they are being sent friend request using firebase cloud messaging, but when the request is sent it returns this error in firebase function log Error: Registration token(s) provided to sendToDevice() must be a non-empty string or a non-empty array. at FirebaseMessagingError.Error (native) at FirebaseMessagingError.FirebaseError [as constructor] (/user_code/node_modules/firebase-admin/lib/utils/error.js:39:28) this is the java-script code i am using
'use strict'
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
exports.sendNotification = functions.database.ref('/Notifications/{user_id}/{notification_id}').onWrite((change, context) => {
c