in TexformField , Null check operator used on a null value flutter

Question

 [my simple program][1]     class _MyHomePageState extends 
 State<MyHomePage> {
String? username;
@override
Widget build(BuildContext context) {
GlobalKey<FormState> formstate =
    new GlobalKey<FormState>(); 

 send() {
 
  var _formdate = formstate.currentState;

  if (_formdate!.validate()) {
    _formdate.save();
    print('valid');
    print('$username');
   } else {
    (print('not valid'));
    print('$username');
    }
   }
   return MaterialApp(
   home: Scaffold(
    appBar: AppBar(
      backgroundColor: Colors.black,
    ),
    body: Form(
      autovalidateMode: AutovalidateMode.always,
      key: formstate, 
      child: Column(
        children: [
          TextFormField(onSaved: (text) {
            username = text;
          }, validator: (text) {
            if (text!.length <= 4) {
              return " text can not be equal or less than 4 characters";
            }
            if (text.length > 10) {
              return "maximum number is 10 characters";
            }
            return "you are correct";
          }),
          RaisedButton(
            onPressed: () {
              send();
            },
            child: const Text('send'),
          ),
         ],
       ),
      ),
     ),
    );
   }
  }

• after running , when i enter valid name and press send, it also gives null and not valid at console, and when remove null check(!) it gives error, don't know how to solve.
• tried to use currentstate.validate and same issue 😖

Answer 1

try

String username = "";

and if this does not work provide more detail on what are you trying to do.

Answer 2

Instead of:

return "you are correct";

write:

return null;