How can I do contextless navigation in order to move to a maintenance screen in Flutter?

I have a Maintenance controller, that initializez an observable variable, and whenever that variable is true, it navigates to a maintenance screen, and when the variable gets set to false it navigates back as follows:

class MaintenanceController extends GetxController {
  RxBool isMaintenance = false.obs;

  @override
  onInit() {
    super.onInit();
    ever(
        isMaintenance,
        (_) => {
              if (isMaintenance.value) {Get.offNamed(Routes.maintenance)} else {Get.offNamed(Routes.splash)}
            });
  }
}

Everything works fine, but I get the following exception in the logs:

flutter: You are trying to use contextless navigation without
a GetMaterialApp or Get.key.
If you are testing your app, you can use:
[Get.testMode = true], or if you are running your app on
a physical device or emulator, you must exchange your [MaterialApp]
for a [GetMaterialApp].
flutter:
#0      GetNavigation.global (package:get/get_navigation/src/extension_navigation.dart:1094:7)
#1      GetNavigation.offNamed (package:get/get_navigation/src/extension_navigation.dart:629:12)
#2      MaintenanceController.onInit.<anonymous closure> (package:n_app/src/screens/maintenance/maintenance_controller.dart:17:85)
#3      ever.<anonymous closure> (package:get/get_rx/src/rx_workers/rx_workers.dart:69:44)
#4      GetStream._notifyData (package:get/get_rx/src/rx_stream/get_stream.dart:47:21)
#5      GetStream.add (package:get/get_rx/src/rx_stream/get_stream.dart:97:5)
#6      RxObjectMixin.value= (package:get/get_rx/src/rx_types/rx_core/rx_impl.dart:105:13)
#7      MaintenanceController.subscribe.<anonymous closure> (package:n_app/src/screens/maintenance/maintenance_controller.dart:29:21)
#8      _rootRunUnary (dart:async/zone.dart:1434:47)
#9      _CustomZone.runUnary (dart:async/zone.dart:1335:19)
#10     _CustomZone.runUnaryGuarded (dart:async/zone.dart:1244:7)
#11     _Bufferi<…>
flutter: ----------------------------------------------------

app.dart:

GetMaterialApp(
      debugShowCheckedModeBanner: false,
      locale: Get.find<LocalizationController>().deviceLocale,
      getPages: Routes.routes,
      localizationsDelegates: AppLocalizations.localizationsDelegates,
      supportedLocales: AppLocalizations.supportedLocales,
      unknownRoute: Routes.getNotFound,
      initialRoute: GetPlatform.isWeb ? Routes.initial : Routes.splash,
      theme: Get.find<ThemeController>().themeData,
      navigatorKey: NavigationService.navigatorKey,
    );

I tried to add the navigatorKey: Get.key and use navigatorKey.currentState!.pushNamed(routeName); to navigate, but the currentState is always null. Any advice?

Adding navigatorKey: Get.key to the GetMaterialApp and continuing to use Get.offNamed(...) instead of navigatorKey.currentState!.pushNamed(routeName); worked.