Flutter List Map not being passed between screens on named route navigation

Question

I am passing data between screens of an app. I have been able to do this successfully with strings but when it comes to sending a List map the Navigator.pushNamed does nothing and doesn't throw any error.

I have my named routes set up like below, in the onGenerateRoute I am taking the settings and passing the arguments to HomePageResultsScreen and ItemPageProfileScreen:

Main.dart:

void main() => runApp(myApp());

class myApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primaryColor: Colors.white,
        ),
        initialRoute: HomePageScreen.id,
        onGenerateRoute: (RouteSettings settings) {

        var routes = <String, WidgetBuilder>{
              HomePageScreen.id: (context) => HomePageScreen(),
              AddItemScreen.id: (context) => AddItemScreen(),
              AdvertiseScreen.id: (context) => AdvertiseScreen(),
              HomePageFilterScreen.id: (context) => HomePageFilterScreen(),
              HomePageResultsScreen.id: (context) => HomePageResultsScreen(settings.arguments),
              ItemPageProfileScreen.id: (context) => ItemPageProfileScreen(settings.arguments),
              ItemPageProfileSuggestUpdateScreen.id: (context) => ItemPageProfileSuggestUpdateScreen(),
              ItemPageWhereToBuyAddStoreToDatabaseScreen.id: (context) => ItemPageWhereToBuyAddStoreToDatabaseScreen(),
              ItemPageWhereToBuyMapScreen.id: (context) => ItemPageWhereToBuyMapScreen(),
              ItemPageWhereToBuyScreen.id: (context) => ItemPageWhereToBuyScreen(),
              MenuScreen.id: (context) => MenuScreen(),
              NotAvailableScreen.id: (context) => NotAvailableScreen(),
              TermsScreen.id: (context) => TermsScreen(),
        };
        WidgetBuilder builder = routes[settings.name];
        return MaterialPageRoute(builder: (ctx) => builder(ctx));

};

When opening the screen I am just sending a string which works fine like this:

Pushing dart file:

onTap: () {Navigator.pushNamed(context, ItemPageProfileScreen.id, arguments: 'myStringData');
          },

and receiving it like this:

Receiving dart file:

class ItemPageProfileScreen extends StatefulWidget {

  final String argument;
  ItemPageProfileScreen(this.argument);

This all works fine. But the problem comes when I try to send a ListMap across.

So I changed my Navigator to push a map like this:

Pushing dart file:

   onTap: () {
                List<Map<String, String>> categoriesMap;
                categoriesMap.add({
                  "category": '',
                  "subCategory1": snapshot.data.documents[index].documentID,
                  "subCategory2": '',
                  "subCategory3": ''});
                Navigator.pushNamed(context, HomePageResultsScreen.id, arguments: categoriesMap);
              },

And then I modified the receiving file to receive the list like this:

Receiving dart file:

class HomePageResultsScreen extends StatefulWidget {

  List<Map<String, String>> arguments;
  HomePageResultsScreen(this.arguments);

But when I try to send the list like this the new screen does not open and no error is shown. What is really weird, If I comment out the the part where I add the categories and just leave it as an empty list map the pushNamed action works and the screen opens. So I am wondering if it is how I am initializing the list map or if there is something else?

Thanks for your help