@Contract(pure=true)
  public static <T> T getOnlyItem(@Nullable Collection<? extends T> items, @Nullable T defaultResult) {
    return items == null || items.size() != 1 ? defaultResult : items.iterator().next();
  }
@Contract(pure=true)
  public static <T> T getOnlyItem(@Nullable Collection<? extends T> items, @Nullable T defaultResult)