@Override
protected Void doInBackground(String... params) {
    Bitmap output = null;
    try {
        URL url = new URL(params[0]);
        Log.d(TAG, "_log: output URL is: "+url.toString());

        HttpURLConnection connection = (HttpURLConnection)url.openConnection();
        connection.setDoInput(true);
        connection.connect();
        InputStream inputStream = connection.getInputStream();
        output = BitmapFactory.decodeStream(inputStream);

        Log.d(TAG, "_log: output size "+output.getByteCount());
    } catch (MalformedURLException e) {
        e.printStackTrace();
        Log.d(TAG, "_log: output with MalformedURLException "+e.toString());
    } catch (IOException e) {
        Log.d(TAG, "_log: output with IOException "+e.toString());
        e.printStackTrace();
    } catch (Exception e) {
        Log.d(TAG, "_log: output with Exception "+e.toString());
        e.printStackTrace();
    } finally {
        if (output != null) util.setupWallpaper(context, output);
        else Log.d(TAG, "_log: output is null");
    }
    return null;
}

output with Exception java.lang.NullPointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getByteCount()' on a null object reference

RetrieveFeed.doInBackground(RetrieveFeed.java:57)
RetrieveFeed.doInBackground(RetrieveFeed.java:27)