How to use scoped_model with Navigator?

Question

I am use scoped_model for manage app state.

I have AuthModel for auth state. When user log in I change screen in AuthModel:

  Widget screen = LoadScreen();

  if (loggedIn == true) {
    screen = HomeScreen;
  } else if (loggedIn == false) {
    screen = LoginScreen;
  }

But I get error when I call in RootPage Widget:

Navigator.of(context).pushReplacementNamed(‘/${model.screen}’); 

‘Package:flutter/src/widgets/navigator.dart’: Failed assertion: line 2106 pos 12: ‘!_debugLocked’: is not true’

RootPage is first page in Flutter app and is use for show load screen until auth return if user is sign in or not:

class RootPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
  return ScopedModelDescendant<AuthModel>(builder: (context, child, model) {
    Navigator.of(context).pushReplacementNamed(‘/${model.screen}’); 
    });
  }
}

Why I am get this error?

How can use scoped_model for do navigation if user is sign in or out?

Thanks!