I am using android studio 3.0 on that when i run App it crashes when i run it on the real device once i click buttonGo . in the code it shows me in yellow line Response.body.toString is reduntant and App crashes and Logcat is indicating me to refer the line when it shows it is reduntant . My logcat is below
 Attempt to invoke virtual method 'java.lang.String java.lang.String.toString()' on a null object reference
                                                                             at com.clone.uber.uberclone.Welcome$4.onResponse(Welcome.java:240)
                                                                             at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)
                                                                             at android.os.Handler.handleCallback(Handler.java:739)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                             at android.os.Looper.loop(Looper.java:135)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5912)
                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                             at java.lang.reflect.Method.invoke(Method.java:372)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405)
                                                                             at com.android.internal.os.ZygoteInit.main
My Java code
    package com.clone.uber.uberclone;
import android.*;
import android.Manifest;
import android.animation.ValueAnimator;
import android.content.pm.PackageManager;
import android.graphics.Color;
import android.location.Location;
import android.os.Handler;
import android.os.SystemClock;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.design.widget.Snackbar;
import android.support.v4.app.ActivityCompat;
import android.support.v4.app.FragmentActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.animation.Interpolator;
import android.view.animation.LinearInterpolator;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.clone.uber.uberclone.Common.Common;
import com.clone.uber.uberclone.Remote.IGoogleAPI;
import com.firebase.geofire.GeoFire;
import com.firebase.geofire.GeoLocation;
import com.github.glomadrian.materialanimatedswitch.MaterialAnimatedSwitch;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.maps.CameraUpdate;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.JointType;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.LatLngBounds;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
import com.google.android.gms.maps.model.Polyline;
import com.google.android.gms.maps.model.PolylineOptions;
import com.google.android.gms.maps.model.SquareCap;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
public class Welcome extends FragmentActivity implements OnMapReadyCallback,
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener,
        LocationListener
{
    private GoogleMap mMap;
    //play services
    private static final int MY_PERMISSION_REQUEST_CODE= 7000;
    private static final int PLAY_SERVICE_RES_REQUEST=7001;
    private LocationRequest mLocationRequest;
    private GoogleApiClient mGoogleApiClient;
    private Location mLastLocation;
    private static int UPDATE_INTERVAL= 5000;
    private static int FASTEST_INTERVAL=3000;
    private static int DISPLACEMENT= 10;
    DatabaseReference drivers;
    GeoFire geoFire;
    Marker mCurrent;
    MaterialAnimatedSwitch location_switch;
    SupportMapFragment mapFragment;
    //car animation
    private List<LatLng> polyLineList;
    private Marker carMarker;
    private float v;
    private double lat,lng;
    private Handler handler;
    private LatLng startPosition,endPosition,currentPosition;
    private int index,next;
    private Button btnGo;
    private EditText edtPlace;
    private String destination;
    private PolylineOptions polylineOptions, blackPolylineOptions;
    private Polyline blackPolyline,greyPolyline;
    private IGoogleAPI mService;
    Runnable drawPathRunnable = new Runnable() {
        @Override
        public void run() {
            if (index<polyLineList.size()-1)
            {
                index++;
                next= index+1;
            }
            if (index<polyLineList.size()-1)
            {
                startPosition = polyLineList.get(index);
                endPosition= polyLineList.get(next);
            }
            ValueAnimator valueAnimator= ValueAnimator.ofFloat(0,1);
            valueAnimator.setDuration(3000);
            valueAnimator.setInterpolator(new LinearInterpolator());
            valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator valueAnimator) {
                    v =valueAnimator.getAnimatedFraction();
                    lng = v*endPosition.longitude+(1-v)*startPosition.longitude;
                    lat = v*endPosition.latitude+(1-v)*startPosition.latitude;
                    LatLng newPos= new LatLng(lat,lng);
                    carMarker.setPosition(newPos);
                    carMarker.setAnchor(0.5f,0.5f);
                    carMarker.setRotation(getBearing(startPosition,newPos));
                    mMap.moveCamera(CameraUpdateFactory.newCameraPosition(
                            new CameraPosition.Builder()
                            .target(newPos)
                            .zoom(15.5f)
                            .build()
                    ));
                }
            });
            valueAnimator.start();
            handler.postDelayed(this,3000);
        }
    };
    private float getBearing(LatLng startPosition, LatLng endPosition) {
        double lat = Math.abs(startPosition.latitude - endPosition.latitude);
        double lng = Math.abs(startPosition.longitude - endPosition.longitude);
        if (startPosition.latitude < endPosition.latitude && startPosition.longitude < endPosition.longitude)
            return (float) (Math.toDegrees(Math.atan(lng/lat)));
        else  if (startPosition.latitude >= endPosition.latitude && startPosition.longitude < endPosition.longitude)
            return (float) ((90-Math.toDegrees(Math.atan(lng/lat)))+90);
        else  if (startPosition.latitude >= endPosition.latitude && startPosition.longitude >= endPosition.longitude)
            return (float) (Math.toDegrees(Math.atan(lng/lat))+180);
        else  if (startPosition.latitude < endPosition.latitude && startPosition.longitude >= endPosition.longitude)
            return (float) ((90-Math.toDegrees(Math.atan(lng/lat)))+270);
        return -1;
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_welcome);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
         mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
        //init view
        location_switch =(MaterialAnimatedSwitch)findViewById(R.id.location_switch);
        location_switch.setOnCheckedChangeListener(new MaterialAnimatedSwitch.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(boolean isOnline) {
                if (isOnline)
                {
                    startLocationUpdates();
                    displayLocation();
                    Snackbar.make(mapFragment.getView(),"you are Online",Snackbar.LENGTH_SHORT).show();
                }
                else
                {
                    stopLocationUpdates();
                    mCurrent.remove();
                    mMap.clear();
                    handler.removeCallbacks(drawPathRunnable);
                    Snackbar.make(mapFragment.getView(),"you are Offline",Snackbar.LENGTH_SHORT).show();
                }
            }
        });
        polyLineList =new ArrayList<>();
        btnGo=(Button)findViewById(R.id.btnGo);
        edtPlace=(EditText)findViewById(R.id.edtPlace);
        btnGo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                destination= edtPlace.getText().toString();
                destination = destination.replace(" ","+"); //replsce space with + for fetch data
                Log.d("WAHDAT",destination);
                getDirection();
            }
        });
        //geo fire
        drivers = FirebaseDatabase.getInstance().getReference("Drivers");
        geoFire=new GeoFire(drivers);
        setUpLocation();
        mService= Common.getGoogleAPI();
    }
    private void getDirection() {
        currentPosition=new LatLng(mLastLocation.getLatitude(),mLastLocation.getLongitude());
        String requestApi =null;
        try{
            requestApi="https://maps.googleapis.com/maps/api/direction/json?"+
                    "mode=driving&"+
                    "transit_routing_preference=less_driving&"+
                    "origin="+currentPosition.latitude+","+currentPosition.longitude+"&"+
                    "destination="+destination+"&"+
                    "key="+getResources().getString(R.string.google_direction_api);
            Log.d("WAHDAT",requestApi); //print url for debug
            mService.getPath(requestApi)
                    .enqueue(new Callback<String>() {
                        @Override
                        public void onResponse(Call<String> call, Response<String> response) {
                            try {
                                JSONObject jsonObject=new JSONObject(response.body().toString());
                                JSONArray jsonArray=jsonObject.getJSONArray("routes");
                                for (int i=0;i<jsonArray.length();i++)
                                {
                                    JSONObject route=jsonArray.getJSONObject(i);
                                    JSONObject poly =route.getJSONObject("overview_polyline");
                                    String polyline=poly.getString("points");
                                    polyLineList=decodePoly(polyline);
                                }
                                //adjusting bounds
                                LatLngBounds.Builder builder=new LatLngBounds.Builder();
                                for (LatLng latLng:polyLineList)
                                    builder.include(latLng);
                                LatLngBounds bounds=builder.build();
                                CameraUpdate mCameraUpdate =CameraUpdateFactory.newLatLngBounds(bounds,2);
                                mMap.animateCamera(mCameraUpdate);
                                polylineOptions = new PolylineOptions();
                                polylineOptions.color(Color.GRAY);
                                polylineOptions.width(5);
                                polylineOptions.startCap(new SquareCap());
                                polylineOptions.endCap(new SquareCap());
                                polylineOptions.jointType(JointType.ROUND);
                                polylineOptions.addAll(polyLineList);
                                greyPolyline = mMap.addPolyline(polylineOptions);
                                blackPolylineOptions = new PolylineOptions();
                                blackPolylineOptions.color(Color.GRAY);
                                blackPolylineOptions.width(5);
                                blackPolylineOptions.startCap(new SquareCap());
                                blackPolylineOptions.endCap(new SquareCap());
                                blackPolylineOptions.jointType(JointType.ROUND);
                                blackPolyline = mMap.addPolyline(blackPolylineOptions);
                                mMap.addMarker(new MarkerOptions().position(polyLineList.get(polyLineList.size()-1))
                                .title("PickUp location"));
                                //Animation
                                ValueAnimator polyLineAnimator =ValueAnimator.ofInt(0,100);
                                polyLineAnimator.setDuration(2000);
                                polyLineAnimator.setInterpolator(new LinearInterpolator());
                                polyLineAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                                    @Override
                                    public void onAnimationUpdate(ValueAnimator valueAnimator) {
                                        List<LatLng> points = greyPolyline.getPoints();
                                        int percentValue=(int)valueAnimator.getAnimatedValue();
                                        int size=points.size();
                                        int newPoints = (int)(size * (percentValue/100.0f));
                                        List<LatLng> p=points.subList(0,newPoints);
                                        blackPolyline.setPoints(p);
                                    }
                                });
                                polyLineAnimator.start();
                                carMarker = mMap.addMarker(new MarkerOptions().position(currentPosition)
                                .flat(true)
                                .icon(BitmapDescriptorFactory.fromResource(R.drawable.car)));
                                handler = new Handler();
                                index=-1;
                                next=1;
                                handler.postDelayed(drawPathRunnable,3000);
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                        }
                        @Override
                        public void onFailure(Call<String> call, Throwable t) {
                      Toast.makeText(Welcome.this,""+t.getMessage(),Toast.LENGTH_SHORT).show();
                        }
                    });
        }catch (Exception e)
        {
            e.printStackTrace();
        }
    }
    private List decodePoly(String encoded) {
        List poly = new ArrayList();
        int index = 0, len = encoded.length();
        int lat = 0, lng = 0;
        while (index < len) {
            int b, shift = 0, result = 0;
            do {
                b = encoded.charAt(index++) - 63;
                result |= (b & 0x1f) << shift;
                shift += 5;
            } while (b >= 0x20);
            int dlat = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
            lat += dlat;
            shift = 0;
            result = 0;
            do {
                b = encoded.charAt(index++) - 63;
                result |= (b & 0x1f) << shift;
                shift += 5;
            } while (b >= 0x20);
            int dlng = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
            lng += dlng;
            LatLng p = new LatLng((((double) lat / 1E5)),
                    (((double) lng / 1E5)));
            poly.add(p);
        }
        return poly;
    }
    //we request runtime permission, we need override onrequestpermissionresult method
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode)
        {
            case MY_PERMISSION_REQUEST_CODE:
                if (grantResults.length >0 && grantResults[0] ==PackageManager.PERMISSION_GRANTED)
                {
                    if (checkPlayServices())
                    {
                        buildGoogleApiClient();
                        createLocationRequest();
                        if (location_switch.isChecked())
                            displayLocation();
                    }
                }
        }
    }
    private void setUpLocation() {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED &&
                ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED)
        {
          //request runtime permission
            ActivityCompat.requestPermissions(this,new String[]{
                    Manifest.permission.ACCESS_COARSE_LOCATION,
                    Manifest.permission.ACCESS_FINE_LOCATION
                    },MY_PERMISSION_REQUEST_CODE);
        }
        else
        {
            if (checkPlayServices())
            {
                buildGoogleApiClient();
                createLocationRequest();
                if (location_switch.isChecked())
                    displayLocation();
            }
        }
    }
    private void createLocationRequest() {
        mLocationRequest =new LocationRequest();
        mLocationRequest.setInterval(UPDATE_INTERVAL);
        mLocationRequest.setFastestInterval(FASTEST_INTERVAL);
        mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
        mLocationRequest.setSmallestDisplacement(DISPLACEMENT);
    }
    private void buildGoogleApiClient() {
        mGoogleApiClient =new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
        mGoogleApiClient.connect();
    }
    private boolean checkPlayServices() {
        int resultCode = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
        if (resultCode != ConnectionResult.SUCCESS) {
            if (GooglePlayServicesUtil.isUserRecoverableError(resultCode))
                GooglePlayServicesUtil.getErrorDialog(resultCode, this, PLAY_SERVICE_RES_REQUEST).show();
            else {
                Toast.makeText(this, "This device is not supported", Toast.LENGTH_SHORT).show();
                finish();
            }
            return false;
        }
        return true;
    }
    private void stopLocationUpdates() {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED &&
                ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED)
        {
            return;
        }
        LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient,this);
    }
    private void displayLocation() {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED &&
                ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED)
        {
            return;
        }
        mLastLocation= LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
        if (mLastLocation !=null)
        {
            if (location_switch.isChecked())
            {
                final double latitude= mLastLocation.getLatitude();
                final double longitude=mLastLocation.getLongitude();
                //update to firebase
                geoFire.setLocation(FirebaseAuth.getInstance().getCurrentUser().getUid(), new GeoLocation(latitude, longitude), new GeoFire.CompletionListener() {
                    @Override
                    public void onComplete(String key, DatabaseError error) {
                        //add marker
                        if (mCurrent !=null)
                           mCurrent.remove();//remove marker already
                       mCurrent = mMap.addMarker(new MarkerOptions()
                                                    .position(new LatLng(latitude,longitude))
                                                               .title("Your Location"));
//
//                        //move camera to this position
                        mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(latitude,longitude),15.0f));
//
                    }
                });
            }
        }
        else
        {
            Log.d("ERROR","Cannot get your Location");
        }
    }
    private void rotateMarker(final Marker mCurrent, final float i, GoogleMap mMap) {
        final Handler handler=new Handler();
        final long start= SystemClock.uptimeMillis();
        final float startRotation = mCurrent.getRotation();
        final long duration = 1500;
        final Interpolator interpolator=new LinearInterpolator();
        handler.post(new Runnable() {
            @Override
            public void run() {
                long elapsed=SystemClock.uptimeMillis() - start;
                float t= interpolator.getInterpolation((float)elapsed/duration);
                float rot= t*i+(1-t)*startRotation;
                mCurrent.setRotation(-rot >180?rot/2:rot);
                if (t<1.0)
                {
                    handler.postDelayed(this,16);
                }
            }
        });
    }
    private void startLocationUpdates() {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED &&
                ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED)
        {
            return;
        }
        LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,mLocationRequest,this);
    }
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
        mMap.setTrafficEnabled(false);
        mMap.setIndoorEnabled(false);
        mMap.setBuildingsEnabled(false);
        mMap.getUiSettings().setZoomControlsEnabled(true);
    }
    @Override
    public void onConnected(@Nullable Bundle bundle) {
displayLocation();
startLocationUpdates();
    }
    @Override
    public void onConnectionSuspended(int i) {
mGoogleApiClient.connect();
    }
    @Override
    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
    }
    @Override
    public void onLocationChanged(Location location) {
    mLastLocation= location;
    displayLocation();
    }
}
 
    