How to set the property pageRouteBuilder of WidgetsApp in Flutter

After poking around in material/app.dart to find how pageRouteBuilder is set there (if using Android Studio, write MaterialApp() anywhere, hover and Ctrl+click once underline appears, then search for 'pageRouteBuilder' in the file that opens), I have found that this can be fixed with

 @override  Widget build(BuildContext context) {    final MaterialPageRoute test = MaterialPageRoute<int>(builder: (context) {      return Container();    });    return new WidgetsApp(        onGenerateRoute: generate,        pageRouteBuilder: <T>(RouteSettings settings, WidgetBuilder builder) {          return MaterialPageRoute(builder: builder, settings: settings);        },        onUnknownRoute: unKnownRoute,        textStyle: const TextStyle(),        initialRoute: "/",        routes: <String, WidgetBuilder>{          '/test': (BuildContext context) => Container(                child: Text('test'),                color: Colors.green,              ),        },        color: Colors.red);  }

If I learn why <T> makes sense in this context in future, I'll edit this and explain as much here.