Firebase Functions app_remove , get userid

I am trying to create a new entry (with userid) in my firebase database as soon as a user removes my app. (Qndroid)

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

exports.appremoved = functions.analytics.event('app_remove').onLog(event => {
  console.log("App remove detected");

  var user = admin.auth().currentUser;
  var uid;

  const uid2 = event.data.user.userId;
  console.log("App remove detected2:" + uid2);

  if (user != null) {
    uid = user.uid;
    console.log("User object not empty" );
    admin.database().ref('/user_events/'+uid + "/"+Date.now()).set("app_remove");
  }
});

I created two variables to get the user id, but both of them are undefined.

uid2 is undefined, and user is null.

I also tried

const user = event.data.user;

But it is also null

How do I get the userid of the user that removed the app?