NullPointerException

protected List<WeatherForecastInfo.ListItem.Weather> list = null;
protected ArrayAdapter<WeatherForecastInfo.ListItem.Weather> adapter = null;

//and in onCreate I have

mapUtil = WeatherUtil.newInstance();
        button.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                new AsyncTask<String, Void, WeatherForecastInfo>() {
                    @Override
                    protected void onPreExecute() {
                        progressDialog = new ProgressDialog(DemoActivity.this);
                        progressDialog.setTitle("Wait...");
                        progressDialog.setMessage("Data is being loaded...");
                        progressDialog.show();
                    }

                    @Override
                    protected WeatherForecastInfo doInBackground(
                            String... params) {

                        return mapUtil.getForecastByCityName(DemoActivity.this, editText.getText().toString(), 2);
                    }
                    @Override
                    protected void onPostExecute(WeatherForecastInfo result) {

                        textView.setText(result.getCity().getName()+ " " + result.getCity().getCountry());
                        list = result.getListItem().getWeather(); // Here Im getting NPE why???
                        adapter = new ArrayAdapter<WeatherForecastInfo.ListItem.Weather>(DemoActivity.this, android.R.layout.simple_list_item_1, list);
                        listView.setAdapter(adapter);
                        progressDialog.dismiss();
                    }
                }.execute(null, null, null);

            }
        });