The minimum setup causes Null check error

[benedict1986]

Describe the bug

When I use the minimum setup, I get Null check operator used on a null value error when enter the credentials and click the login button

To Reproduce
Steps to reproduce the behavior:

Use the following code

class UserAuthenticationPage extends StatelessWidget {
  const UserAuthenticationPage({super.key});

  @override
  Widget build(BuildContext context) {
    return FlutterLogin(onLogin: (_) async {
      return '';
    }, onRecoverPassword: (_) async {
      return '';
    });
  }
}

and enter the credentails and click the login button, I am given the Null check operator used on a null value error with the stacktrace

E/flutter (11025): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Null check operator used on a null value
E/flutter (11025): #0      AuthCardState._changeToCard.<anonymous closure>.<anonymous closure> (package:flutter_login/src/widgets/cards/auth_card_builder.dart:350:41)
E/flutter (11025): <asynchronous suspension>

Expected behavior

Nothing should be done because there is no implementation in login function

Screenshots

Information (please complete the following information):

• Device: Nexus 5 API 33 emulator
• Platform: Android mobile
• Flutter version: 3.10.2
• Package version: 4.1.1

Additional context

N/A