NoSuchMethodError: invalid member on null: 'toList' (Flutter Web) An exception was throw by _MapStream

The error: NoSuchMethodError: invalid member on null: 'toList comes, but code works when I use the commented provider i.e. final userdetails = Provider.of<List>(context).toList() ?? [];

However, if I use final userdetails = Provider.of<List>(context).toList() ?? []; I get this two errors, and app displays red screen. 1- NoSuchMethodError: invalid member on null: 'toList 2- An exception was throw by _MapStream<QuerySnapshot, List> listened by

import 'package:traveltogether_admin/Admin_Screens/Admin_ManageUsers_Tile.dart';
import 'package:traveltogether_admin/Models/user.dart';

class ManageUsers extends StatelessWidget {
  static const id = 'Admin_manage_users';
  @override
  Widget build(BuildContext context) {
    final userdetails = Provider.of<List<MyUserData>>(context).toList() ?? [];
    // final userdetails = Provider.of<List<RequestToJoinData>>(context).toList() ?? [];
    final user= userdetails;
    return ListView.builder(
        // shrinkWrap: true,
        // physics: NeverScrollableScrollPhysics(),
        // primary: false,
        itemCount: userdetails.length,
        itemBuilder: (context,index)
    {
      print(userdetails);
          return ManageUserTile(user[index]);
    });
  }
}