Flutter error : The method 'save' isn't defined for the type 'State'

Can anybody help me resolving this ?

I'm trying to do a simple Form in flutter but since I'm using a new version of flutter (2.0.2)

I've got this error message : The method 'save' isn't defined for the type 'State'. Try correcting the name to the name of an existing method, or defining a method named 'save'.

Code :

import 'package:flutter/material.dart';

class AddressFormScreen extends StatefulWidget {
  AddressFormScreen();

  @override
  _AddressFormScreenState createState() => _AddressFormScreenState();
}

class _AddressFormScreenState extends State<AddressFormScreen> {
  final GlobalKey formKey = GlobalKey<FormState>();

  void _saveForm() {
    formKey.currentState!.save();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        child: Form(
      key: formKey,
      child: TextFormField(),
    ));
  }
}