getSmsCodeFromUser function Null safety

Implementation

Future<String?> getSmsCodeFromUser(BuildContext context) async {
  String? smsCode;

  // Update the UI - wait for the user to enter the SMS code
  await showDialog<String>(
    context: context,
    barrierDismissible: false,
    builder: (context) {
      return AlertDialog(
        title: const Text('SMS code:'),
        actions: [
          ElevatedButton(
            onPressed: () {
              Navigator.of(context).pop();
            },
            child: const Text('Sign in'),
          ),
          OutlinedButton(
            onPressed: () {
              smsCode = null;
              Navigator.of(context).pop();
            },
            child: const Text('Cancel'),
          ),
        ],
        content: Container(
          padding: const EdgeInsets.all(20),
          child: TextField(
            onChanged: (value) {
              smsCode = value;
            },
            textAlign: TextAlign.center,
            autofocus: true,
          ),
        ),
      );
    },
  );

  return smsCode;
}