مشکل در پروژه مارکت

بعد از ساخت لیست ویو در آموزش پروژه مارکت و موقع نمایشش ارورهای زیر رو میده

FATAL EXCEPTION: main

java.lang.RuntimeException: Unable to start activity ComponentInfo{ir.seyyed.course.androidmarket/ir.seyyed.course.androidmarket.ApplicationsList}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference

at ir.seyyed.course.androidmarket.AdapterApplication.<init>(AdapterApplication.java:0)
                                                                                  at ir.seyyed.course.androidmarket.ApplicationsList.onCreate(ApplicationsList.java:23)

 کلاس  ApplicationList: 

public class ApplicationsList extends Activity {

  private ListView list;
  private AdapterApplication adapter;
  private ArrayList<StructApplication> applications = new ArrayList<StructApplication>();

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

    adapter = new AdapterApplication(applications);
    list = (ListView) findViewById(R.id.lstview);
    list.setAdapter(adapter);

    populateDataFake();

  }

  private void populateDataFake(){
    for (int i =1 ; i< 51; i++){
      StructApplication application = new StructApplication();
      application.name = "Application #" + i;
      application.price = (int) ((Math.random() *10)+20)*100;
      application.ratingValue = (float) (Math.random() * 5);

      applications.add(application);
    }

    adapter.notifyDataSetChanged();
  }


}

خط23:  

adapter = new AdapterApplication(applications);

کلاس AdapterApplication:

public class AdapterApplication extends ArrayAdapter<StructApplication> {



  public AdapterApplication(ArrayList<StructApplication> array) {
    super(G.context, R.layout.adapter_list, array);
  }


  private static class ViewHolder {

    public ViewGroup layoutRoot;
    public TextView  txtName;
    public TextView  txtPrice;
    public ImageView imgLogo;
    public RatingBar rating;


    public ViewHolder(View view) {
      layoutRoot = (ViewGroup) view.findViewById(R.id.layoutRoot);
      txtName = (TextView) view.findViewById(R.id.txtName);
      txtPrice = (TextView) view.findViewById(R.id.txtPrice);
      imgLogo = (ImageView) view.findViewById(R.id.imgApp);
      rating = (RatingBar) view.findViewById(R.id.rating);
    }


    public void fill(final ArrayAdapter<StructApplication> adapter, final StructApplication item, final int position) {
      txtName.setText(item.name);
      txtPrice.setText("" + item.price );
      rating.setRating(item.ratingValue);


    }
  }


  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;

    StructApplication item = getItem(position);
    if (convertView == null) {
      convertView = G.inflater.inflate(R.layout.adapter_list, parent, false);
      holder = new ViewHolder(convertView);
      convertView.setTag(holder);
    } else {
      holder = (ViewHolder) convertView.getTag();
    }

    holder.fill(this, item, position);
    return convertView;
  }
}