public static <E> ImmutableMultiset<E> of(E e1) {
    return copyFromElements(e1);
  }

  /**
   * Returns an immutable multiset containing the given elements, in order.
   *
   * @throws NullPointerException if any element is null
   * @since 6.0 (source-compatible since 2.0)
   */
  public static <E> ImmutableMultiset<E> of(E e1, E e2) {
    return copyFromElements(e1, e2);
  }

  /**