onTapConfirm method Null safety

Implementation

void onTapConfirm(BuildContext context, String username) async {
  if (_isSubmitting) return;
  _isSubmitting = true;

  final String code = confirmController.text.trim();
  if (code.isEmpty) {
    EventService().eventBus.fire(PopupEvent(
        type: PopupType.alert,
        action: PopupAction.show,
        data: {"title": "오류", "content": "코드를 입력하세요."},
        onClose: () {
          Navigator.of(context, rootNavigator: true).popUntil((route) => !route.settings.name!.startsWith(PopupScreen.routeName));
        }));
    _isSubmitting = false;
    return;
  }

  try {
    SignUpResult result = await Amplify.Auth.confirmSignUp(username: username, confirmationCode: code);
    if (result.isSignUpComplete) {
      EventService().eventBus.fire(PopupEvent(
          type: PopupType.alert,
          action: PopupAction.show,
          data: {"title": "성공", "content": "계정인증에 성공했습니다. 로그인을 진행해주세요."},
          onClose: () {
            Navigator.of(context, rootNavigator: true).popUntil((route) => route.settings.name == SplashScreen.routeName);
            Navigator.of(context, rootNavigator: true).pushNamed(SignInScreen.routeName);
          }));
    }
  } on AuthException catch (e) {
    EventService().eventBus.fire(PopupEvent(
        type: PopupType.alert,
        action: PopupAction.show,
        data: {"title": "오류", "content": e.message},
        onClose: () {
          Navigator.of(context, rootNavigator: true).popUntil((route) => !route.settings.name!.startsWith(PopupScreen.routeName));
        }));
  }
  _isSubmitting = false;
}