Sign up does not work

[czmirek]

I'm following README.md but I'm getting this error when I want to sign up a new user.

E/flutter (12487): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: Invalid argument (onError): Error handler must accept one Object or one Object and a StackTrace as arguments.: Closure: (HttpException) => Null
E/flutter (12487): #0      Stream.handleError (dart:async/stream.dart:666:7)
E/flutter (12487): #1      IOClient.send (package:http/src/io_client.dart:48:20)
E/flutter (12487): <asynchronous suspension>
E/flutter (12487): #2      BaseClient._sendUnstreamed (package:http/src/base_client.dart:176:32)
E/flutter (12487): <asynchronous suspension>
E/flutter (12487): #3      _withClient (package:http/http.dart:166:12)
E/flutter (12487): <asynchronous suspension>
E/flutter (12487): #4      _MyAppState.getUserDetails (package:flutterdemo/main.dart:149:36)
E/flutter (12487): <asynchronous suspension>
E/flutter (12487): #5      _MyAppState.loginAction (package:flutterdemo/main.dart:181:11)
E/flutter (12487): <asynchronous suspension>
E/flutter (12487): #6      Login.build.<anonymous closure> (package:flutterdemo/main.dart:86:13)
E/flutter (12487): <asynchronous suspension>
E/flutter (12487):