_TypeError (Null check operator used on a null value) _onGenerateRoute

I have this main.dart code:

@override  Widget build(BuildContext context) {    bool isUserLoggedin = false;    return FutureBuilder(        future: _checkLoginStatus(),        builder: (context, snapshot) {          if (snapshot.connectionState == ConnectionState.done) {            isUserLoggedin = snapshot.data as bool;            return MaterialApp(              supportedLocales: L10n.all,              locale: _locale,              localizationsDelegates: const [                AppLocalizations.delegate,                GlobalMaterialLocalizations.delegate,                GlobalCupertinoLocalizations.delegate,                GlobalWidgetsLocalizations.delegate,              ],              initialRoute: isUserLoggedin ? '/home' : '/login',              routes: {'/home': (context) => HomePage(),'/login': (context) => Login(),              },            );          } else {            return MaterialApp(              home: Scaffold(                body: Center(child: Text('loading')),              ),            );          }        });  }

and i am facing this error:

Exception has occurred._TypeError (Null check operator used on a null value)

in this code in app.dart:

PlatformRouteInformationProvider? _defaultRouteInformationProvider;  BackButtonDispatcher get _effectiveBackButtonDispatcher =>      widget.backButtonDispatcher ?? _defaultBackButtonDispatcher!;  RootBackButtonDispatcher? _defaultBackButtonDispatcher;  // NAVIGATOR  GlobalKey<NavigatorState>? _navigator;  Route<dynamic>? _onGenerateRoute(RouteSettings settings) {    final String? name = settings.name;    final WidgetBuilder? pageContentBuilder =        name == Navigator.defaultRouteName && widget.home != null            ? (BuildContext context) => widget.home! //error is here            : widget.routes![name];    if (pageContentBuilder != null) {      assert(        widget.pageRouteBuilder != null,'The default onGenerateRoute handler for WidgetsApp must have a ''pageRouteBuilder set if the home or routes properties are set.',      );      final Route<dynamic> route = widget.pageRouteBuilder!<dynamic>(        settings,        pageContentBuilder,      );      return route;

While running my code in debugging mode, I encountered a situation where it gets stuck in a particular section. The error originates from a file named app.dart, which was not authored by me. My main.dart file contains my code, and I am unsure which specific code in app.dart is causing the error.