How to send image to server (PHP) from android?

Question

PHP

You need to do the following:
1) the user selects an image from the gallery
2) this image is sent to the server
3) the image is stored on the
Android server:

private class ConnectToServer extends AsyncTask<Void, Void, Integer> {

        HttpURLConnection conn;
        Integer res;

        protected Integer doInBackground(Void... params) {

            try {
                Intent photoPickerIntent = new Intent(Intent.ACTION_PICK);
                photoPickerIntent.setType("image/*");
                startActivityForResult(photoPickerIntent, 1);


                HttpRequest request = HttpRequest.post("http://potatosing.16mb.com/index.php");
                request.part("image", "image.jpg", new File(mUri.getPath()));


                URL url = new URL(request.body());
                conn = (HttpURLConnection) url.openConnection();
                conn.setConnectTimeout(1000000);
                conn.setRequestMethod("POST");
                conn.setRequestProperty("User-Agent", "Mozilla/5.0");
                conn.connect();

                Toast.makeText(getApplicationContext(), url.getFile(), Toast.LENGTH_SHORT).show();
            } catch (Exception e) {

            }
            return res;
        }
    }

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent imageReturnedIntent) {
        super.onActivityResult(requestCode, resultCode, imageReturnedIntent);

        if (resultCode == RESULT_OK) {
            mUri = imageReturnedIntent.getData();
        }

    }
}

In this line:

request.part("image", "image.jpg", new File(mUri.getPath()));

getPath() returns null
Actually the questions are:
1) why it returns null
2) how to send this image correctly
3) how to "accept" this image in php and save it
PS: To make a post request I used: https://github.com/kevinsawicki/ http-request
PSS: I'm completely new, and please be understanding)
Thanks in advance)