我做了一个在谷歌地图上显示当前位置的活动，它不起作用，我似乎无法找出原因？

如何解决我做了一个在谷歌地图上显示当前位置的活动，它不起作用，我似乎无法找出原因？

public class GrayMapsActivity extends AppCompatActivity implements OnMapReadyCallback {
private GoogleMap mMap;
LocationManager locationManager;
public Location currentlocation;
public String s1,s2;
public Double d1,d2;
TextView txt1,txt2;
private FusedLocationProviderClient fusedLocationClient;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
    d1=0.0;
    d2=0.0;
    super.onCreate(savedInstanceState);
    fusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
    setContentView(R.layout.activity_gray_maps_activity);
    SupportMapFragment mapFragment = (SupportMapFragment) 
    getSupportFragmentManager().findFragmentById(R.id.map);
    assert mapFragment != null;
    mapFragment.getMapAsync(this);
    txt1 = (TextView) (findViewById(R.id.textView1));
    txt2 = (TextView) (findViewById(R.id.textView2));
    if (ActivityCompat.checkSelfPermission(this,Manifest.permission.ACCESS_FINE_LOCATION) != 
    PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this,Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        return;
    }
    fusedLocationClient.getLastLocation()
            .addOnSuccessListener(this,new OnSuccessListener<Location>() {
                @Override
                public void onSuccess(Location location) {
                    // Got last kNown location. In some rare situations this can be null.
                    if (location != null) {
                        d1= location.getLatitude();
                        d2= location.getLongitude();
                    }
                }
            });

}

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
   LatLng graycarlocation= new LatLng(d1,d2);
            mMap.addMarker(new MarkerOptions()
                   .position(graycarlocation)
                    .title("Gray Car Location"));
    mMap.moveCamera(CameraUpdateFactory.newLatLng(graycarlocation));

  }


  }

“这是主要活动，我使用融合位置来获取最后一个已知位置，然后将其插入到双变量中的经度和纬度，由于某种原因，当地图开始时它不会到达该位置，

出现的错误代码： 尝试在空对象引用上调用虚拟方法“double java.lang.Double.doubleValue()” "