Refresh Listview simpleCursorAdapter always null

I have a program with fills a listview from a SQLLiteDB. The initialload works, but when I edit a entry the program crashes and the simplecursorAdapter = null.

The Fragment:

public class TaskListFragment extends ListFragment
{
DBHelper dbHelper;
SimpleCursorAdapter simpleCursorAdapter;
Cursor cursor;
ListView listView;
static final int UPDATE_TASK = 1;
String[] from = {dbHelper.COL_2,dbHelper.COL_3};
int[] to = new int[]{R.id.taskName , R.id.taskDescription};


public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    View rootView = inflater.inflate(R.layout.tasklistlayout, container, false);

    listView = (ListView)rootView.findViewById(android.R.id.list);

    setRetainInstance(true);
    retu rootView;
}

@Override
public void onActivityCreated(Bundle savedInstanceState)
{
    super.onActivityCreated(savedInstanceState);
    dbHelper = new DBHelper(getActivity());
    prepareCursor();
}

public void prepareCursor()
{
    new Handler().post(new Ruable()
    {
        @Override
        public void run()
        {
            cursor = dbHelper.getTasksForListView();
            simpleCursorAdapter = new SimpleCursorAdapter (getActivity(),R.layout.taskrowlayout,cursor,from,to,0);
            fillList();
        }
    });
}

public void updateList()
{
    simpleCursorAdapter.notifyDataSetChanged();
    fillList();
}

public void fillList()
{
    setListAdapter(simpleCursorAdapter);
}

@Override
public void onListItemClick(ListView l, View v, int position, long id)
{
    Intent intent = new Intent(getActivity().getApplicationContext(), TaskInformation.class);
    intent.putExtra("taskId", cursor.getInt(0));
    intent.putExtra("taskName", cursor.getString(1));
    intent.putExtra("taskDescription", cursor.getString(2));
    intent.putExtra("taskStartDate", cursor.getString(3));
    intent.putExtra("taskEndDate", cursor.getString(4));
    startActivityForResult(intent, UPDATE_TASK);
}
}

The piece of code in MainActivity wich calls it:

   @Override
public void onActivityResult(int requestCode, int resultCode, Intent data)
{
        if (resultCode == RESULT_OK)
        {
            taskListFragment.updateList();
        }
}

The code in the TaskInformation class witch runs when i click update

    public void updateTask(View view)
{
    task = new ArrayList<>();
    task.add(0,String.valueOf(currentTaskId));
    task.add(1,String.valueOf(taskName.getText()));
    task.add(2,String.valueOf(taskDescription.getText()));
    task.add(3,String.valueOf(startDate.getText()));
    task.add(4,String.valueOf(endDate.getText()));
    dbHelper.updateTask(task);
    setResult(RESULT_OK, intent);
    finish();
}

The result retu nicely and the code arives in the onresult method. But why is the simpleCursorAdapter always NULL when I update it? I want to refresh/reload the listview when I updated it.