Flutterfire: iOS - Linking anonymous account with email provider results in exception "The method '[]' was called on null."

[erparker]

The problem

I am attempting to link an anonymous user with an email/password credential and I am consistently getting this exception thrown

NoSuchMethodError: The method '[]' was called on null.
Receiver: null
Tried calling: []("isNewUser")

the relevant flutter code:

Future<FirebaseUser> linkWithEmailPassword(String email, String password) async {
    AuthCredential credential = EmailAuthProvider.getCredential(email: email, password: password);
    AuthResult auth = await currentUser.linkWithCredential(credential);
    if (auth.user != null) {
      print("Linking accounts succeeded");
      return auth.user;
    } else {
      print("** /n/n LINKING ANONYMOUS ACCOUNT FAILED /n/n **");
      return null;
    }
  }

neither of my print statements above ever execute, I get an exception from Firebase, which I am catching, and that's where it stops. In other words, the call to Firebase's linkWithCredential is what is returning an error.

I am also double checking that currentUser is indeed anonymous.

One strange thing about this is that a new email/password account is created every time. Sometimes the accounts are even linked, but not in every case.

I am using:

cloud_firestore: ^0.12.11
firebase_auth: ^0.15.1
firebase_storage: ^3.0.8

What I am not doing

I am not creating a new user with the credentials before trying to link them. I tried that for fun and it always gives me back an error about the account already being linked to that provider type, but never this exception.

What I have tried

flutter clean
flutter pub get

pod update Firebase/Firestore
pod update Firebase/FirebaseAuth

I have tried downgrading cloud firestore 0.12.0 since someone said their crash started in 0.12.11, but that didn't work either

Flutter Doctor

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel dev, v1.13.0, on Mac OS X 10.14.6 18G84, locale en-US)

[!] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
    ! Some Android licenses not accepted.  To resolve this, run: flutter doctor --android-licenses
[✓] Xcode - develop for iOS and macOS (Xcode 11.1)
[✓] Android Studio (version 3.5)
[✓] VS Code (version 1.32.1)
[✓] Connected device (1 available)

! Doctor found issues in 1 category.

[jahngergely]

In my case simple anonymous login fails with the same error message, only in iOS. I think the root of the problem is that firebase_auth_platform_interface doesn't prepared for null additionalUserInfo. The interface was implemented for flutter web compatibility. The plugin was fixed in version 0.12.0 to handle null additionalUserInfo, so downgrading firebase_auth is a possible workaround. The interface was added in 0.15.0+2.
firebase_auth: 0.15.0+1works for me.

PlatformAuthResult _decodeAuthResult(Map<dynamic, dynamic> data) {
  final PlatformUser user = _decodeUser(data['user']);
  final PlatformAdditionalUserInfo additionalUserInfo =
      _decodeAdditionalUserInfo(data['additionalUserInfo']);
  return PlatformAuthResult(user: user, additionalUserInfo: additionalUserInfo);
}

PlatformAdditionalUserInfo _decodeAdditionalUserInfo(
    Map<dynamic, dynamic> data) {
  return PlatformAdditionalUserInfo(
    isNewUser: data['isNewUser'],    **// IF data == null EXCEPTION**
    username: data['username'],
    providerId: data['providerId'],
    profile: data['profile']?.cast<String, dynamic>(),
  );

}

[iapicca]

Hi @erparker
can you please provide your flutter run --verbose?
Also, to better address the issue, would be helpful
if you could post a minimal code sample
or the steps to reproduce the problem.
Thank you

[erparker]

I posted the code in my original question that's giving me the error. Basically I have an anonymous user and I try to link with an email credential and then this exception happens. I'll post some more code for added context.

Here's the --verbose error. The first line is my code preparing to make the link call and the last line is the exception I get from the library.
verbose-error.txt

[erparker]

My plan is to allow users to have an anonymous login and later convert to a permanent user. So on app launch I am checking for any user, if I don't find one I login anonymously, and I keep a reference to the current user in a helper class:

class FirebaseAuthMethods {
  static final FirebaseAuthMethods instance = FirebaseAuthMethods._private();

  FirebaseAuthMethods._private();

  factory FirebaseAuthMethods() => instance;

  final FirebaseAuth _firebaseAuth = FirebaseAuth.instance;

  FirebaseUser currentUser;

...  

Future<FirebaseUser> anonymousLogin() async {
    try {
      AuthResult auth = await _firebaseAuth.signInAnonymously();
      print("anonymous login with user: ${auth.user}");
      currentUser = auth.user;
      return currentUser;
    } catch (e) {
      print("error doing anonymous login: $e");
    }
    return null;
  }

Later on my login/signup page I am simply gathering the user's email and password, creating a credential, and then trying to link the anonymous account with the email/password credential. I am checking to see if the user is indeed anonymous before trying to link the accounts, and the user always is.

if (widget.auth.currentUser.isAnonymous == true) {
            print("account is anonymous, attempting link");
            await widget.auth.linkWithEmailPassword(_email, _password);
          } else {
            print("attempting to sign up new user, not anonymous");
            userId = await widget.auth.signUp(_email, _password);
            print("signed up new user: $userId");
          }

...

Future<FirebaseUser> linkWithEmailPassword(String email, String password) async {
    AuthCredential credential = EmailAuthProvider.getCredential(email: email, password: password);
    AuthResult auth = await currentUser.linkWithCredential(credential);
    if (auth.user != null) {
      print("Linking accounds succeeded");
      return auth.user;
    } else {
      // TODO: Linking accounts fails if the credential was already linked to another user accounts
      // In this case we must merge accounts manually
      print("** /n/n LINKING ANONYMOUS ACCOUNT FAILED /n/n **");
      return null;
    }
  }

I get the exception on the line AuthResult auth = await currentUser.linkWithCredential(credential);, the if-else clause right after that never runs, always fails on linkWithCredential.

@iapicca I am happy to provide more context or code samples if it will help!

[erparker]

@jahngergely Yeah, I have been able to login anonymously without any issues across all the versions of the firebase_auth library I've used. My problem is linking the anonymous account with a email/password credential. I just tried the 0.15.0+1 version and I got the same error.

also, @iapicca I read on someone's StackOverflow response that in order to link email/password credentials to another user, you have to allow for multiple accounts per email. Is that true? Either way, I turned that option on but that didn't fix the issue for me.

[collinjackson]

Fix will be landing soon (see #1588).

[hterkelsen]

Fix landed. Please run pub upgrade and verify that this fixes your issue!

[jsonthor]

@hterkelsen I can confirm this works - had the same issue, ran flutter pub upgrade tonight and it's working like a charm.

[erparker]

oh whoops I meant to respond to the update
@hterkelsen same as the previous comment, running flutter pub upgrade solved the issue for me. Things are working great!

thanks for the lightning fast response to this one! 🎉