Flutter when using GlobalKey "The method '...' was called on null error"

Question

I have a contacts application in Flutter. I call a function in my ContactListPage statefull class using GlobalKey in another class called PushMessageManager. When I delete the application and run it for the first time and a notification comes to the application, I get the error "The method 'refreshContactsFromServer' was called on null". However, when I close the application and open it again, the function works as I want.

I wonder what I'm missing? Any ideas on how I can solve this? My codes are as follows:

final contactListPageKey = GlobalKey<ContactListPageState>();

      routes: <String, WidgetBuilder>{
        '/login': (BuildContext context) => LoginScene(),
        '/contactList': (context) => ContactListPage(key: contactListPageKey),
        '/contact': (context) => ContactPage(),
      },

    FirebaseMessaging.onMessage.listen((RemoteMessage remoteMessage) async {
      if (remoteMessage.data.isNotEmpty) {
        if (remoteMessage.data["type"] == "message") {
          await contactListPageKey.currentState.refreshContactsFromServer();
          print("Contacts are updated.");
        }
}

I tried methods such as FutureDelayed and await but nothing changes.

Future.delayed(const Duration(seconds: 1), () {
   contactListPageKey.currentState.refreshContactsFromServer();
});