Getting XML for xmlpullparser with AsyncTask

Question

I want to download XML file from some URL and use it like input for my XMLPullParser.

So I wrote AsyncTask for downloading XML and call it in my code, but I have got NullPointerException:

java.lang.RuntimeException: Unable to start activity java.lang.NullPointerException: Attempt to invoke interface method 'void org.xmlpull.v1.XmlPullParser.setInput(java.io.InputStream, java.lang.String)' on a null object reference

Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'void org.xmlpull.v1.XmlPullParser.setInput(java.io.InputStream, java.lang.String)' on a null object reference

Here starts my Activity and AsynTask:

public class Parsing extends AppCompatActivity {
    private final static String url = "http://validURL";
    InputStream parserInput;
    XmlPullParser parser;

    protected void onCreate(Bundle savedInstanceState) {
...
        try {
            parserInput = new GetXML(this).execute(url).get();
            parser.setInput(parserInput,null);
        } catch (ExecutionException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (XmlPullParserException e) {
            e.printStackTrace();
        }
...
}
    class GetXML extends AsyncTask<String, Void, InputStream> {
        private Parsing activity;
        private String url;
        private ProgressDialog pDialog;

        public GetXML(Parsing activity/*, String url*/) {
            this.activity = activity;
//            this.url = url;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(activity);
            pDialog.setTitle("Getting XML");
            pDialog.setMessage("Loading...");
            pDialog.show();
        }

        @Override
        protected InputStream doInBackground(String... params) {
            try {
                URL url = new URL(this.url);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setReadTimeout(10000 /* milliseconds */);
                connection.setConnectTimeout(15000 /* milliseconds */);
                connection.setRequestMethod("GET");
                connection.setDoInput(true);
                connection.connect();
                InputStream stream = connection.getInputStream();

                stream.close();
                return stream;

            } catch (Exception e) {
                e.printStackTrace();
                Log.e("AsyncTask", "exception");
                return null;
            }
        }

        @Override
        protected void onPostExecute(InputStream result) {
            pDialog.dismiss();
        }
    }


}

What is wrong in my code?

Why I am getting NullPointer exception instead of loading xml and setting it like input data for XMLPullParser?

UPD:

XML is big - about 6-8Mb.

So according to: What is a NullPointerException, and how do I fix it?

I should use ... = null; where I have not initialize object? Or I shouldn't use it?

UPD 2:

after initializing InputStream parserInput = null; I am getting the same error.