Android Studio Project with Java, Parse and Heroku

Question

I am a beginner programmer and have started to re-program Uber. Unfortunately I always get the same error in one class. Can anyone help me?

I am desperate and hope to find help here.

Error code

07-07 15:02:12.600 2809-2809/com.parse.starter E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.parse.starter, PID: 2809
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewTreeObserver android.widget.RelativeLayout.getViewTreeObserver()' on a null object reference
    at com.parse.starter.ViewRiderLocation.onMapReady(ViewRiderLocation.java:121)
    at com.google.android.gms.maps.SupportMapFragment$zza$1.zza(Unknown Source)
    at com.google.android.gms.maps.internal.zzo$zza.onTransact(Unknown Source)
    at android.os.Binder.transact(Binder.java:499)
    at de.b(:com.google.android.gms.dynamite_mapsdynamite@202117052@20.21.17 (040700-0):2)
    at com.google.maps.api.android.lib6.impl.be.run(:com.google.android.gms.dynamite_mapsdynamite@202117052@20.21.17 (040700-0):2)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6119)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Source code

public class ViewRiderLocation extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;
    Intent i;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view_rider_location);

        i = getIntent();

        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }


    public void back(View view){
        Intent i = new Intent(getApplicationContext(), ViewRequests.class);
        startActivity(i);
    }


    public void acceptRequest(View view){

        Log.i("MyApp", "Request Accepted");

        ParseQuery<ParseObject> query = new ParseQuery<ParseObject>("Requests");
        query.whereEqualTo("requesterUserName", i.getStringExtra("username"));

        query.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> objects, ParseException e) {

                if(e == null){
                    Log.i("MyApp", "found in Background");
                    if(objects.size() >0){

                        Log.i("MyApp", "Objects found");
                        for(ParseObject object : objects){

                            object.put("driverUsername", ParseUser.getCurrentUser().getObjectId());
                            object.saveInBackground(new SaveCallback() {
                                @Override
                                public void done(ParseException e) {
                                    Log.i("MyApp","driverUsername Saved");
                                    if(e == null){
                                        Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://maps.google.com/maps?daddr=" + i.getDoubleExtra("latitude",0) + "," + i.getDoubleExtra("longitude", 0)));
                                        startActivity(intent);

                                    }
                                }
                            });
                        }
                    }

                }
            }

        });
    }


    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        RelativeLayout mapLayout = (RelativeLayout)findViewById(R.id.relativeLayout);

        mapLayout.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener(){
            @Override
            public void onGlobalLayout() {

                LatLngBounds.Builder builder = new LatLngBounds.Builder();

                ArrayList<Marker> markers = new ArrayList<Marker>();

                markers.add(mMap.addMarker(new MarkerOptions().position(new LatLng(i.getDoubleExtra("latitude", 0), i.getDoubleExtra("longitude", 0))).icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE)).title("Rider")));
                markers.add(mMap.addMarker(new MarkerOptions().position(new LatLng(i.getDoubleExtra("userLatitude", 0), i.getDoubleExtra("userLongitude", 0))).title("Deine Position")));

                for(Marker marker: markers){
                    builder.include(marker.getPosition());
                }

                LatLngBounds bounds = builder.build();

                int padding = 100;
                CameraUpdate cu = CameraUpdateFactory.newLatLngBounds(bounds, padding);
                mMap.animateCamera(cu);

            }
        });
    }
}