[ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: type 'Null' is not a subtype of type 'String' in type cast
#0 _$_$CustomTokenSignInResponseFromJson (package:firebase_auth_rest/src/models/signin_response.g.dart:106:30)
#1 new _$CustomTokenSignInResponse.fromJson (package:firebase_auth_rest/src/models/signin_response.freezed.dart:1703:7)
#2 RestApi.signInWithCustomToken (package:firebase_auth_rest/src/rest_api.dart:99:33)
<asynchronous suspension>
#3 FirebaseAuth.signInWithCustomToken (package:firebase_auth_rest/src/firebase_auth.dart:209:9)
<asynchronous suspension>
_$CustomTokenSignInResponse _$_$CustomTokenSignInResponseFromJson(
Map<String, dynamic> json) {
return _$CustomTokenSignInResponse(
idToken: json['idToken'] as String,
refreshToken: json['refreshToken'] as String,
expiresIn: json['expiresIn'] as String,
localId: json['localId'] as String, // <<<< NPE
);
}