Android : Error publishing Facebook custom story from Android App

i am trying to post a custom story. So far i created a a new story on the open graph section of the developer section. the action is "votar" and the object is "Encuesta", the namespace is "idkl_sharetest".

the following are two functions, the first one is to publish an image on the wall and is working fine.

public void postImage() {
        if (checkPermissions()) {
            Bitmap img = BitmapFactory.decodeResource(getResources(),
                    R.drawable.ic_launcher);
            Request uploadRequest = Request.newUploadPhotoRequest(
                    Session.getActiveSession(), img, new Request.Callback() {
                        @Override
                        public void onCompleted(Response response) {
                            Toast.makeText(MainActivity.this,
                                    "Photo uploaded successfully",
                                    Toast.LENGTH_LONG).show();
                        }
                    });
            uploadRequest.executeAsync();
        } else {
            requestPermissions();
        }
    }

the second one is to publish a custom story (image, title, description) and the app closes.

public void postStory() {
    if (checkPermissions()) {

    try {

        RequestBatch requestBatch = new RequestBatch();

         Bundle imageParams = new Bundle();
        Bitmap image = BitmapFactory.decodeResource(this.getResources(),
                    R.drawable.logo);
        imageParams.putParcelable("file", image);

        Request.Callback imageCallback = new Request.Callback() {

                @Override
                public void onCompleted(Response response) {
                    FacebookRequestError error = response.getError();
                    if (error != null) {
                        Toast.makeText(MainActivity.this,
                                "Error1" + error,
                                Toast.LENGTH_LONG).show();
                        Log.i(TAG, error.getErrorMessage());
                    }
                }
        };

        Request imageRequest = new Request(Session.getActiveSession(),
                    "me/staging_resources", imageParams,
                    HttpMethod.POST, imageCallback);

        imageRequest.setBatchEntryName("imageUpload");

        requestBatch.add(imageRequest);

        JSONObject encuesta = new JSONObject();
        encuesta.put("image", "{result=imageUpload:$.uri}");
        encuesta.put("title", "Nueva encuesta");
        encuesta.put("type", "encuesta.other");
        encuesta.put("description", "Texto para nueva encuesta");

        Bundle objectParams = new Bundle();
        objectParams.putString("object", encuesta.toString());

        Request.Callback objectCallback = new Request.Callback() {

            @Override
            public void onCompleted(Response response) {
                FacebookRequestError error = response.getError();
                if (error != null) {
                    Toast.makeText(MainActivity.this,
                            "Error2" + error,
                            Toast.LENGTH_LONG).show();
                    Log.i(TAG, error.getErrorMessage());
                }
            }
        };

        Request objectRequest = new Request(Session.getActiveSession(),
                "me/objects/encuesta.other", objectParams,
                HttpMethod.POST, objectCallback);

        objectRequest.setBatchEntryName("objectCreate");

        requestBatch.add(objectRequest);

        Bundle actionParams = new Bundle();
        actionParams.putString("other", "{result=objectCreate:$.id}");
        actionParams.putString("fb:explicitly_shared", "true");

        Request.Callback actionCallback = new Request.Callback() {

            @Override
            public void onCompleted(Response response) {

                FacebookRequestError error = response.getError();
                if (error != null) {
                    Toast.makeText(MainActivity.this,
                            "Error3" + error,
                            Toast.LENGTH_LONG).show();
                } else {
                    String actionId = null;
                    try {
                        JSONObject graphResponse = response
                                .getGraphObject()
                                .getInnerJSONObject();
                        actionId = graphResponse.getString("id");
                    } catch (JSONException e) {
                        Log.i(TAG,
                                "JSON error "+ e.getMessage());
                    }
                    Toast.makeText(getApplicationContext(),
                            actionId,
                            Toast.LENGTH_LONG).show();
                }
            }
        };

        Request actionRequest = new Request(Session.getActiveSession(),
                "me/idkl_sharetest:votar", actionParams, HttpMethod.POST,
                actionCallback);

        requestBatch.add(actionRequest);

        requestBatch.executeAsync();
    } catch (JSONException e) {
        Log.i(TAG,
                "JSON error "+ e.getMessage());
    }


} else {
    requestPermissions();
}

}

running the app on Android Virtual Device gets the following error code

03-20 18:46:38.995: E/AndroidRuntime(1102): FATAL EXCEPTION: main 03-20 18:46:38.995: E/AndroidRuntime(1102): Process: com.example.sharetest, PID: 1102 03-20 18:46:38.995: E/AndroidRuntime(1102): java.lang.NullPointerException 03-20 18:46:38.995: E/AndroidRuntime(1102): at com.example.sharetest.MainActivity$8.onCompleted(MainActivity.java:219) 03-20 18:46:38.995: E/AndroidRuntime(1102): at com.facebook.Request$4.run(Request.java:1668) 03-20 18:46:38.995: E/AndroidRuntime(1102): at android.os.Handler.handleCallback(Handler.java:733) 03-20 18:46:38.995: E/AndroidRuntime(1102): at android.os.Handler.dispatchMessage(Handler.java:95) 03-20 18:46:38.995: E/AndroidRuntime(1102): at android.os.Looper.loop(Looper.java:136) 03-20 18:46:38.995: E/AndroidRuntime(1102): at android.app.ActivityThread.main(ActivityThread.java:5017) 03-20 18:46:38.995: E/AndroidRuntime(1102): at java.lang.reflect.Method.invokeNative(Native Method) 03-20 18:46:38.995: E/AndroidRuntime(1102): at java.lang.reflect.Method.invoke(Method.java:515) 03-20 18:46:38.995: E/AndroidRuntime(1102): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 03-20 18:46:38.995: E/AndroidRuntime(1102): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 03-20 18:46:38.995: E/AndroidRuntime(1102): at dalvik.system.NativeStart.main(Native Method)

thanks for helping