@SuppressWarnings("NonApiType") // acts as a direct substitute for a constructor call
  public static <E extends @Nullable Object> HashSet<E> newHashSet(Iterable<? extends E> elements) {
    return (elements instanceof Collection)
        ? new HashSet<E>((Collection<? extends E>) elements)
        : newHashSet(elements.iterator());
  }

  /**
   * Creates a <i>mutable</i> {@code HashSet} instance containing the given elements. A very thin