code: public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4, E e5, E e6,
        E... others) {
      final int paramCount = 6;
      Object[] elements = new Object[paramCount + others.length];
      elements[0] = e1;
      elements[1] = e2;
      elements[2] = e3;
      elements[3] = e4;
      elements[4] = e5;
      elements[5] = e6;
      System.arraycopy(others, 0, elements, paramCount, others.length);
      return construct(elements.length, elements);
    }
docs: Returns an immutable set containing the given elements, in order. Repeated
  occurrences of an element (according to {@link Object#equals}) after the
  first are ignored.
  
  @throws NullPointerException if any element is null
  @since 3.0 (source-compatible since 2.0)