失败的断言：第 35 行 pos 18：'longitude != null'：不是真的

Question

我仍在尝试使用我的出租车应用程序。我应该在何处搜索下车地点，但每次用户搜索一个地点并使用 Google 自动完成点击它时，它不断出现此错误：

[ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: 'package:google_maps_flutter_platform_interface/src/types/location.dart': Failed assertion: line 35 pos 18: 'longitude != null': is not true. 

我曾尝试使用 FutureBuilder 小部件，因为该应用程序依赖于等待另一个无效的操作完成。应用程序仍然崩溃，因此其他方法没有执行。 这是错误指向的方法：

  Future<void> getPlaceDirection() async
  {
    var initialPos = Provider.of<AppData>(context, listen: false).pickUpLocation;
    var finalPos = Provider.of<AppData>(context, listen: false).dropOffLocation;

    var pickUpLatLng = LatLng(initialPos.latitude, initialPos.longitude);
    var dropOffLatLng = LatLng(finalPos.latitude, finalPos.longitude);

    showDialog(
      context: context, 
      builder: (BuildContext content) => ProgressDialog(message: "Please wait...",)
    );
    var details = await AssistantMethods.obtainPlaceDirectionDetails(pickUpLatLng, dropOffLatLng);

    setState(() {
          tripDirectionDetails = details;
        });
    Navigator.pop(context);

    print("This is encoded points :");
    print(details.encodedPoints);

    PolylinePoints polylinePoints = PolylinePoints();
    List<PointLatLng> decodedPolyLinePointsResult = polylinePoints.decodePolyline(details.encodedPoints);
     
    pLineCoordinates.clear();

    if (decodedPolyLinePointsResult.isNotEmpty)
    {
      decodedPolyLinePointsResult.forEach((PointLatLng pointLatLng)
      {
         pLineCoordinates.add(LatLng(pointLatLng.latitude, pointLatLng.longitude));
      });
    }

    polylineSet.clear();

    setState(() {
     Polyline polyline = Polyline(
      color: orange,
      polylineId: PolylineId("PolylineID"),
      jointType: JointType.round,
      points: pLineCoordinates,
      width: 5,
      startCap: Cap.roundCap,
      endCap: Cap.roundCap,
      geodesic: true,
      );

      polylineSet.add(polyline);
        });

      LatLngBounds latLngBounds;
      if(pickUpLatLng.latitude > dropOffLatLng.latitude && pickUpLatLng.longitude > dropOffLatLng.longitude)
      {
        latLngBounds = LatLngBounds(southwest: dropOffLatLng, northeast: pickUpLatLng);
      }
      else if(pickUpLatLng.longitude> dropOffLatLng.longitude)
      {
        latLngBounds = LatLngBounds(southwest: LatLng(pickUpLatLng.latitude, dropOffLatLng.longitude), 
        northeast: LatLng(dropOffLatLng.latitude, pickUpLatLng.longitude));
      }
      else if(pickUpLatLng.latitude > dropOffLatLng.latitude)
      {
        latLngBounds = LatLngBounds(southwest: LatLng(dropOffLatLng.latitude, pickUpLatLng.longitude), 
        northeast: LatLng(pickUpLatLng.latitude, dropOffLatLng.longitude));
      } 
      else 
      {
        latLngBounds = LatLngBounds(southwest: pickUpLatLng, northeast: dropOffLatLng);
      }

      newGoogleMapController.animateCamera(CameraUpdate.newLatLngBounds(latLngBounds, 70));

      Marker pickUpLocMarker = Marker(
        icon: BitmapDescriptor.defaultMarkerWithHue(BitmapDescriptor.hueBlue),
        infoWindow: InfoWindow(title: initialPos.placeName, snippet: "My location"),
        position:  pickUpLatLng,
        markerId: MarkerId("pickUpId"),
      );

      Marker dropOffLocMarker = Marker(
        icon: BitmapDescriptor.defaultMarkerWithHue(BitmapDescriptor.hueRed),
        infoWindow: InfoWindow(title: finalPos.placeName, snippet: "Drop-off location"),
        position:  dropOffLatLng,
        markerId: MarkerId("dropOffId"),
      );

      setState(() {
              markerSet.add(pickUpLocMarker);
              markerSet.add(dropOffLocMarker);
            });

      Circle pickUpLocCircle = Circle(
        fillColor: Colors.blue,
        center: pickUpLatLng,
        radius: 12,
        strokeWidth: 4,
        strokeColor: Colors.blueAccent,
        circleId: CircleId("pickUpId")
      );

      Circle dropOffLocCircle = Circle(
        fillColor: Colors.red,
        center: dropOffLatLng,
        radius: 12,
        strokeWidth: 4,
        strokeColor: Colors.redAccent,
        circleId: CircleId("dropOffId"),
      ); 

      setState(() {
              circleSet.add(pickUpLocCircle);
              circleSet.add(dropOffLocCircle);
            }); 
  }