@NotNull ModalityStateEx appendEntity(@NotNull Object anEntity){
    List<@NotNull Object> modalEntities = getModalEntities();
    List<Object> list = new ArrayList<>(modalEntities.size() + 1);
    list.addAll(modalEntities);
    list.add(anEntity);
    return new ModalityStateEx(list);
  }
@NotNull ModalityStateEx appendEntity(@NotNull Object anEntity)