I get this EXCEPTION when navigating about flutter_google_places HOT 1 CLOSED

 String birthPlace = await Navigator.of(context).push(
          MaterialPageRoute(
            builder: (BuildContext context) => WillPopScope(
                  onWillPop: requestPop,
                  child: CustomSearchScaffold(),
                ),
          ),
        );

import 'dart:async';

import 'package:flutter_google_places_autocomplete/flutter_google_places_autocomplete.dart';
import 'package:flutter/material.dart';

const kGoogleApiKey = "myrealapikey";

GoogleMapsPlaces _places = GoogleMapsPlaces(kGoogleApiKey);

final searchScaffoldKey = GlobalKey<ScaffoldState>();

Future<Null> displayPrediction(Prediction p, ScaffoldState scaffold) async {
  if (p != null) {
    PlacesDetailsResponse detail = await _places.getDetailsByPlaceId(p.placeId);
    print('detail $detail');
    var lat = detail.result.geometry.location.lat;
    var lng = detail.result.geometry.location.lng;
    print("${p.description} $lat/$lng ");
    Navigator.of(scaffold.context).pop("${p.description}");

    scaffold
        .showSnackBar(SnackBar(content: Text("${p.description} $lat/$lng ")));
  }
}

class CustomSearchScaffold extends GooglePlacesAutocompleteWidget {
  static const String routeName = 'places';
  CustomSearchScaffold()
      : super(apiKey: kGoogleApiKey, language: "en", components: [
          Component(Component.country, "in"),
          Component(Component.country, "us"),
        ]);

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

class _CustomSearchScaffoldState extends GooglePlacesAutocompleteState {
  @override
  Widget build(BuildContext context) {
    final appBar = AppBar(
      titleSpacing: 20.0,
      automaticallyImplyLeading: false,
      title: AppBarPlacesAutoCompleteTextField(),
      backgroundColor: Color.fromRGBO(57, 73, 171, 1.0),
    );
    final body = GooglePlacesAutocompleteResult(onTap: (p) {
      // displayPrediction(p, searchScaffoldKey.currentState);
    });
    return Scaffold(key: searchScaffoldKey, appBar: appBar, body: body);
  }

  @override
  void onResponseError(PlacesAutocompleteResponse response) {
    super.onResponseError(response);
    searchScaffoldKey.currentState
        .showSnackBar(SnackBar(content: Text(response.errorMessage)));
  }

  @override
  void onResponse(PlacesAutocompleteResponse response) {
    super.onResponse(response);
    if (response != null && response.predictions.isNotEmpty) {
      searchScaffoldKey.currentState
          .showSnackBar(SnackBar(content: Text("Got answer")));
    }
  }
}