Error dialog comes up for me!

package com.rachitagarwal.blogreader;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.AlertDialog;
import android.app.ListActivity;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.text.Html;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;

public class MainListActivity extends ListActivity {

    public static final int NUMBER_OF_POSTS = 20;
    public static final String BLOG_URL = "http://blog.teamtreehouse.com/api/get_recent_summary/?count=";
    public static final String TAG = MainListActivity.class.getSimpleName();
    protected JSONObject mBlogData;
    protected ProgressBar mProgressBar;

    private final String KEY_TITLE = "title";
    private final String KEY_AUTHOR = "author";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_list);

        mProgressBar = (ProgressBar) findViewById(R.id.progressBar1);

        if (isNetworkAvailable()) {
            mProgressBar.setVisibility(View.VISIBLE);
            GetBlogPostsTask getBlogPostsTask = new GetBlogPostsTask();
            getBlogPostsTask.execute();
        }
        else {
            Toast.makeText(this, "Network is unavailable!", Toast.LENGTH_LONG).show();
        }

        //Toast.makeText(this, getString(R.string.no_items), Toast.LENGTH_LONG).show();
    }

    private boolean isNetworkAvailable () {
        ConnectivityManager manager = (ConnectivityManager) getSystemService (Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = manager.getActiveNetworkInfo();
        boolean isAvailable = false;
        if(networkInfo!=null && networkInfo.isConnected()) {
            isAvailable = true;
        }
        return isAvailable;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    public void handleBlogResponse() {
        mProgressBar.setVisibility(View.INVISIBLE);

        if (mBlogData==null) {
            updateDisplayForError();
        }
        else {
            try {
                //Log.d(TAG, mBlogData.toString(2));
                JSONArray jsonPosts = mBlogData.getJSONArray("posts");
                ArrayList<HashMap<String, String>> blogPosts = new ArrayList<HashMap<String, String>>();


                for (int i=0; i<jsonPosts.length(); i++) {
                    JSONObject post = jsonPosts.getJSONObject (i);

                    String title = post.getString(KEY_TITLE);
                    title = Html.fromHtml(title).toString();
                    String author = post.getString(KEY_AUTHOR);
                    author = Html.fromHtml(author).toString();

                    HashMap<String, String> blogPost = new HashMap<String, String>();
                    blogPost.put(KEY_TITLE, title);
                    blogPost.put(KEY_AUTHOR, author);

                    blogPosts.add(blogPost);
                }

                String[] keys = { KEY_TITLE, KEY_AUTHOR };
                int[] ids = { android.R.id.text1, android.R.id.text2 };
                SimpleAdapter adapter = new SimpleAdapter (this, blogPosts, android.R.layout.simple_list_item_2, keys, ids);
                setListAdapter (adapter);

            } catch (JSONException e) {
                Log.e(TAG, "Exception caught: ", e);
            }
        }

    }

    private void updateDisplayForError() {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle(getString(R.string.error_title));
        builder.setMessage(getString(R.string.error_message));
        builder.setPositiveButton(android.R.string.ok, null);
        AlertDialog dialog = builder.create();
        dialog.show();

        TextView emptyTextView = (TextView) getListView().getEmptyView();
        emptyTextView.setText(getString(R.string.no_items));
    }

    private class GetBlogPostsTask extends AsyncTask<Object, Void, JSONObject> {
        @Override
        protected JSONObject doInBackground (Object... arg0) {
            int responseCode = -1;
            JSONObject jsonResponse = null;

            try {
                URL blogFeedUrl = new URL(BLOG_URL + NUMBER_OF_POSTS);
                HttpURLConnection connection = (HttpURLConnection) blogFeedUrl.openConnection();
                connection.connect();

                responseCode = connection.getResponseCode();
                if (responseCode==HttpURLConnection.HTTP_OK) {
                    InputStream inputStream = connection.getInputStream();
                    Reader reader = new InputStreamReader(inputStream);
                    int contentLength = connection.getContentLength();
                    char[] charArray = new char[contentLength];
                    reader.read(charArray);
                    String responseData = new String (charArray);
                    Log.v(TAG, responseData);

                    jsonResponse = new JSONObject (responseData);
                    /*
                    String status = jsonResponse.getString ("status");
                    Log.v(TAG, status);
                    JSONArray jsonPosts = jsonResponse.getJSONArray("posts");
                    for (int i = 0; i<jsonPosts.length(); i++) {
                        JSONObject jsonPost = jsonPosts.getJSONObject(i);
                        String title = jsonPost.getString ("title");
                        Log.v(TAG, "Post " + i + ": " + title);
                    }*/
                }
                else {
                Log.i(TAG, "Unsuccessful HTTP Response Code: " + responseCode);
                }
            }
            catch(MalformedURLException e) {
                Log.e(TAG, "MalformedURLException caught: ", e);
            }
            catch (IOException e) {
                Log.e(TAG, "IOException caught: ", e);
            }
            catch (Exception e) { 
                Log.e(TAG, "Exception caught: ", e);
            }

            return jsonResponse;
        }

        @Override
        protected void onPostExecute (JSONObject result) {
            mBlogData = result;
            handleBlogResponse();
        }
    }
}