return (ImmutableList<E>) EMPTY;
  }

  /**
   * Returns an immutable list containing a single element. This list behaves and performs
   * comparably to {@link Collections#singletonList}, but will not accept a null element. It is
   * preferable mainly for consistency and maintainability of your code.
   *
   * @throws NullPointerException if {@code element} is null
   */

    return (ImmutableList<E>) EMPTY;
  }

  /**
   * Returns an immutable list containing a single element. This list behaves and performs
   * comparably to {@link Collections#singletonList}, but will not accept a null element. It is
   * preferable mainly for consistency and maintainability of your code.
   *
   * @throws NullPointerException if {@code element} is null
   */