AsyncQueryHandler onQueryComplete Listener is NULL

I am using AsyncQueryHandler in getview(); Each item in getview() make Async Query . But Sometimes onqueryComplete() returns null.

protected void onQueryComplete(int token, Object cookie, Cursor cursor) {
    final AsyncQueryListener listener = mListener.get();
    if (listener != null) {
        listener.onQueryComplete(token, cookie, cursor);
    } else if (cursor != null) {
        cursor.close();
    }
}

what is the reason behind it?