code: public static <E> HashSet<E> newHashSet(Iterator<? extends E> elements) {
      HashSet<E> set = newHashSet();
      Iterators.addAll(set, elements);
      return set;
    }
docs: Creates a <i>mutable</i> {@code HashSet} instance containing the given elements. A very thin
  convenience for creating an empty set and then calling {@link Iterators#addAll}.
  
  <p><b>Note:</b> if mutability is not required and the elements are non-null, use {@link
  ImmutableSet#copyOf(Iterator)} instead.
  
  <p><b>Note:</b> if {@code E} is an {@link Enum} type, you should create an {@link EnumSet}
  instead.
  
  <p>Overall, this method is not very useful and will likely be deprecated in the future.