Android. Fragment getActivity() sometime returns null
===

In developer console error reports sometime I see  reports with NPE issue. I have no understand what is wrong with my code. On emulator and my device application works good without forcecloses, however some users get NullPointerException in fragment class when calls getActivity() method.

Activity

    pulic class MyActivity extends FragmentActivity{
	
	private ViewPager pager; 
	private TitlePageIndicator indicator;
	private TabsAdapter adapter;
	
	 @Override
    public void onCreate(Bundle savedInstanceState) {
		
		pager = (ViewPager) findViewById(R.id.pager);;
		indicator = (TitlePageIndicator) findViewById(R.id.indicator);
		adapter = new TabsAdapter(getSupportFragmentManager(), false);
			
		adapter.addFragment(new FirstFragment());
        adapter.addFragment(new SecondFragment());
        indicator.notifyDataSetChanged();
        adapter.notifyDataSetChanged();

		// push first task
		FirstTask firstTask = new FirstTask(MyActivity.this);
		// set first fragment as listener
        firstTask.setTaskListener((TaskListener) adapter.getItem(0));
        firstTask.execute();
		
	}
	
	 indicator.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                Fragment currentFragment = adapter.getItem(position);
                ((Taskable) currentFragment).executeTask();
            }

            @Override
            public void onPageScrolled(int i, float v, int i1) {}

            @Override
            public void onPageScrollStateChanged(int i) {}
     });
}

    
AsyncTask class

    public class FirstTask extends AsyncTask{

	private TaskListener taskListener;

	...
	
	@Override
    protected void onPostExecute(T result) {
	   ...	
       taskListener.onTaskComplete(result);
    }
	
}


Fragment class

    public class FirstFragment extends Fragment immplements Taskable, TaskListener{


	public FirstFragment() {
    }
	
	
	@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.first_view, container, false);;
    }
	
	@Override
    public void executeTask() {
        FirstTask firstTask = new FirstTask(MyActivity.this);
        firstTask.setTaskListener(this);
        firstTask.execute();
    }

	
	@Override
    public void onTaskComplete(T result) {
		// NPE is here 
        Resources res = getActivity().getResources();
		...
    }

}


Maybe this error happens when applications resumed from background. In this case how I should handle this situation properly?