@Override
    public PsiFile @NotNull [] findFilesWithTodoItems() {
      // a hack here with _todo filter
      TodoFilter todoFilter = getTodoTreeStructure().getTodoFilter();

      Set<TodoItem> todoItems = doFindAllTodoItems(todoFilter);
      buildMap(todoItems);

      synchronized (myMap) {
        final Set<PsiFile> files = myMap.keySet();
        return files.toArray(PsiFile.EMPTY_ARRAY);
      }
    }
@Override
    public PsiFile @NotNull [] findFilesWithTodoItems()