Android : Error with Picasa API JSON request - org.json.JSONException: End of input at character 0 of

I am trying to GET a JSON response from Picasa API but caught the error:

org.json.JSONException: End of input at character 0 of

Request URL: https://picasaweb.google.com/data/feed/api/user/kodingralph?kind=album&alt=json

My code:

JsonObjectRequest jsonObjReq = new JsonObjectRequest(url, null,
            new Response.Listener<JSONObject>() {

        @Override
        public void onResponse(JSONObject response) {
            Log.d(TAG, "Albums Response: " + response);
            List<Category> albums = new ArrayList<Category>();
            try {
                JSONArray entry = response.getJSONObject(TAG_FEED)
                        .getJSONArray(TAG_ENTRY);

                for (int i = 0; i < entry.length(); i++) {
                    JSONObject albumObj = (JSONObject) entry.get(i);
                    String albumId = albumObj.getJSONObject(
                            TAG_GPHOTO_ID).getString(TAG_T);
                    String albumTitle = albumObj.getJSONObject(
                            TAG_ALBUM_TITLE).getString(TAG_T);

                    Category album = new Category();
                    album.setId(albumId);
                    album.setTitle(albumTitle);

                    albums.add(album);

                    Log.d(TAG, "Album Id: " + albumId
                            + ", Album Title: " + albumTitle);
                }

                controllerApp.getInstance().getPrefManger()
                        .storeCategories(albums);

                Intent intent = new Intent(getApplicationContext(),
                        MainActivity.class);
                startActivity(intent);
                finish();

            } catch (JSONException e) {
                e.printStackTrace();
                Toast.makeText(getApplicationContext(),
                        getString(R.string.msg_unknown_error),
                        Toast.LENGTH_LONG).show();
            }

        }
    }, new Response.ErrorListener() {

        @Override
        public void onErrorResponse(VolleyError error) {
            Log.e(TAG, "Volley Error: " + error.getMessage());
            Toast.makeText(getApplicationContext(),
                    getString(R.string.splash_error),
                    Toast.LENGTH_LONG).show();
        }
    });