Firebase: Get the parent of a snapshot.

firebase_snapshot_parent.js

function getParent(snapshot) {
  // You can get the reference (A Firebase object) from a snapshot
  // using .ref().
  var ref = snapshot.ref();
  // Now simply find the parent and return the name.
  return ref.parent().name();
}

var testRef = new Firebase("https://example.firebaseIO-demo.com/foo/bar");
testRef.once("value", function(snapshot) {
  // Should alert "Name of the parent: foo".
  alert("Name of the parent: " + getParent(snapshot));
});

Hi everyone i have a big problem about my function it has an error and this it says: Error: function crashed. Details: Registration token(s) provided to sendToDevice() must be a non-empty string or a non-empty array.

And this is my code:

`const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

exports.sendNewEmergencyNotification = functions.database.ref('messages/{id}').onCreate(event=>{

console.log('User to send notification');

var ref = admin.database().ref(`users/allusers/${pushId}/token`);
return ref.once("value", function(snapshot){
     const payload = {
          notification: {
              title: 'An Emergency has been Reported!!',
              body: 'Tap here to view details..'
          }
     };

     admin.messaging().sendToDevice(snapshot.val(), payload)

}, function (errorObject) {
    console.log("The read failed: " + errorObject.code);
});

})`

thank you in advance

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