title: Flutter FCM getToken() returns null
body: <p>FCM <code>getToken()</code> always returns null on real devices, but is working just fine on emulator, I don't know what causes this. Here's how I use <code>getToken()</code>:</p>
  <pre><code>FirebaseMessaging _firebaseMessaging = FirebaseMessaging();
  String fcmToken = &quot;&quot;;
  await _firebaseMessaging.getToken().then((value) async {
    fcmToken = value;
    if (fcmToken != &quot;&quot;) {
      await _userCollection.doc(user.id).set({
        'email': user.email,
        'name': user.name,
        'noHp': user.noHp,
        'alamat': user.alamat,
        &quot;email_verification&quot;: user.emailVerification,
        &quot;phone_verification&quot;: user.phoneVerification,
        &quot;device_token&quot;: fcmToken,
      });
    }
    return;
  });
  </code></pre>
  <p>The real device that I use is Android Marshmallow.</p>