@Override
  public <T extends Content> List<T> getContent(@NotNull Filter<T> filter) {
    List<T> result = new ArrayList<>();
    for (Object it : myContent) {
      if (filter.matches(it)) {
        //noinspection unchecked
        result.add((T)it);
      }
    }
    return result;
  }
@Override
  public <T extends Content> List<T> getContent(@NotNull Filter<T> filter)