Blog Reader App ERROR

public static final int NUMBER_OF_POSTS = 20;
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);
        GetBlogPostTasks getBlogPostTasks = new GetBlogPostTasks();
        getBlogPostTasks.execute();
    }

    else{
        Toast.makeText(this, "Network not available", Toast.LENGTH_LONG).show();

    }

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

}

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);
    try {
        JSONArray jsonPosts =  mBlogData.getJSONArray("posts");
        JSONObject jsonPost = jsonPosts.getJSONObject(position);
        String blogUrl = jsonPost.getString("url");
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setData(Uri.parse(blogUrl));
        startActivity(intent);
    } catch (JSONException e) {
        logException(e);
    }
}

private void logException(Exception e) {
    Log.e(TAG, "Exception Caught", e);
}

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;     
}


public void handleBlogResponse() {
    mProgressBar.setVisibility(View.INVISIBLE);
    if (mBlogData == null){         
        updateDisplayForError();
    }
    else {
        try {
            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) {
            logException(e);
        }

    }

}

private void updateDisplayForError() {
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setTitle(getString(R.string.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));
}


//Async Task
private class GetBlogPostTasks extends AsyncTask<Object, Void, JSONObject>{

    @Override
    protected JSONObject doInBackground(Object... arg0) {
        int responseCode = -1;
        JSONObject jsonResponse =  null;

        try {
            //setting a URL variable
            URL blogFeedUrl = new URL("http://blog.teamtreehouse.com/api/get_recent_summary/?count=" + NUMBER_OF_POSTS);

            //Linking URL variable to connection manager
            HttpURLConnection connection = (HttpURLConnection) blogFeedUrl.openConnection();

            //Connecting URL
            connection.connect();

            //Getting HTTP connection ResponseCode (200:Success 400:Failure)
            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);

                jsonResponse = new JSONObject(responseData);            
            }
            else{
                Log.i(TAG, "Code: " + responseCode);
            }

        }
        catch(MalformedURLException e){
             logException(e);
        }
        catch(IOException e){
            logException(e);
        }
        catch(Exception e){
            logException(e);
        }
        return jsonResponse;
    }

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


}

@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);
}