创建Android的RSSReader时出错

Question

我正在尝试创建一个RSS阅读器，以便从Google新闻的RSS源中读取。这是我的代码：

import android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;


public class ReadRss extends AsyncTask<Void, Void, Void> {
    Context context;
    String address = "https://news.google.co.uk/news?cf=all&hl=en&pz=1&ned=uk&output=rss";
    ProgressDialog progressDialog;
    URL url;

    public ReadRss(Context context) {
        this.context = context;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        progressDialog.dismiss();
    }

    @Override
    protected Void doInBackground(Void... params) {
        ProcessXml(Getdata());

        return null;
    }

    private void ProcessXml(Document data) {
        if (data != null) {
            ArrayList<FeedItem>feedItems=new ArrayList<>();
            Element root = data.getDocumentElement();
            Node channel = root.getChildNodes().item(1);
            NodeList items = channel.getChildNodes();
            for (int i = 0; i < items.getLength(); i++) {
                Node cureentchild = items.item(i);
                if (cureentchild.getNodeName().equalsIgnoreCase("item")) {
                    FeedItem item=new FeedItem();
                    NodeList itemchilds = cureentchild.getChildNodes();
                    for (int j = 0; j < itemchilds.getLength(); j++) {
                        Node cureent = itemchilds.item(j);
                        if (cureent.getNodeName().equalsIgnoreCase("title")){
                            item.setTitle(cureent.getTextContent());
                        }else if (cureent.getNodeName().equalsIgnoreCase("description")){
                            item.setDescription(cureent.getTextContent());
                        }else if (cureent.getNodeName().equalsIgnoreCase("pubDate")){
                            item.setPubDate(cureent.getTextContent());
                        }else if (cureent.getNodeName().equalsIgnoreCase("link")){
                            item.setLink(cureent.getTextContent());
                        }
                    }
                    feedItems.add(item);
                    Log.d("itemTitle", item.getTitle());
                    Log.d("itemDescription",item.getDescription());
                    Log.d("itemPubDate",item.getPubDate());
                    Log.d("itemLink",item.getLink());



                }
            }
        }
    }

    public Document Getdata() {
        try {
            url = new URL(address);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            InputStream inputStream = connection.getInputStream();
            DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = builderFactory.newDocumentBuilder();
            Document xmlDoc = builder.parse(inputStream);
            return xmlDoc;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }
}

但是当我尝试运行时，我收到此错误：

Attempt to invoke interface method 'org.w3c.dom.NodeList org.w3c.dom.Node.getChildNodes()' on a null object reference

我不知道为什么它是null。我是新手，所以非常感谢帮助。