issue with Getx navigation

Question

In terminal get this error message

**The following _CastError was thrown while handling a gesture: Null check operator used on a null value

When the exception was thrown, this was the stack: #0 PageRedirect.page (package:get/get_navigation/src/routes/route_middleware.dart:199:50) #1 GetMaterialApp.generator (package:get/get_navigation/src/root/get_material_app.dart:337:73) #2 _WidgetsAppState._onGenerateRoute (package:flutter/src/widgets/app.dart:1371:37) #3 NavigatorState._routeNamed (package:flutter/src/widgets/navigator.dart:3998:46) #4 NavigatorState.pushNamed (package:flutter/src/widgets/navigator.dart:4055:20) #5 GetNavigation.toNamed (package:get/get_navigation/src/extension_navigation.dart:595:37) #6 _HomeScreenState.build.. (package:task_react/screens/home_screen/home_screen.dart:38:21) #7 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:198:24) #8 TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:608:11) #9 BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:296:5) #10 BaseTapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:267:7) #11 GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:157:27) #12 GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:443:20) #13 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:419:22) #14 RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:322:11) #15 GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:374:7) #16 GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:338:5) #17 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:296:7) #18 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:279:7) #22 _invoke1 (dart:ui/hooks.dart:169:10) #23 PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:293:7) #24 _dispatchPointerDataPacket (dart:ui/hooks.dart:88:31) (elided 3 frames from dart:async)

Handler: "onTap" Recognizer: TapGestureRecognizer#4572b

**

while trying to navigate from one HomeScreen to BookDetailScreen. I am simply passing constant string as argument. I tried changing get: ^4.6.1 to get: 4.5.1 in pubsec.yaml file too. Still having same issue. Any help would be highly appreciated.

home_screen

class HomeScreen extends StatefulWidget {
  static const route = "/home_screen";
  const HomeScreen({ Key key }) : super(key: key);

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}
class _HomeScreenState extends State<HomeScreen> {
  @override
  void initState() {
    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white54,
      appBar: AppBar(title: const Text("ITBook"),),
      body: SizedBox(

        child: GridView.builder(
          shrinkWrap: true,
          gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 2,mainAxisSpacing: 2, crossAxisSpacing: 2,
          childAspectRatio: 1/1.4,),
          scrollDirection: Axis.vertical,
            itemCount: 10,
            itemBuilder: (context, index) => InkWell(
              onTap:(){
                const String isbn = "testing";
                Get.toNamed(DetailScreen.route,arguments: [isbn]);
              },
              child: Container(
                color: Colors.white,
              ),
              ),
              ),
     
      ),
      
    );
  }
}

detail_screen simply displays the text for now

class DetailScreen extends StatefulWidget {
  static const route = "/detail_screen";
   final String isbn = Get.arguments[0];


  @override
  _DetailScreenState createState() => _DetailScreenState();
}

class _DetailScreenState extends State<DetailScreen> {
  @override
  void initState() {    
    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Container(
          child: Text(widget.isbn),
        ),
      ),
      
    );
  }
}