code: public static <E> ImmutableSet<E> copyOf(E[] elements) {
      switch (elements.length) {
        case 0:
          return of();
        case 1:
          return of(elements[0]);
        default:
          return construct(elements.length, elements.clone());
      }
    }
docs: Returns an immutable set containing each of {@code elements}, minus duplicates, in the order
  each appears first in the source array.
  
  @throws NullPointerException if any of {@code elements} is null
  @since 3.0