* Builder} and its comparator.
     */
    @Override
    public ImmutableSortedSet<E> build() {
      @SuppressWarnings("unchecked") // we're careful to put only E's in here
      E[] contentsArray = (E[]) contents;
      ImmutableSortedSet<E> result = construct(comparator, size, contentsArray);
      this.size = result.size(); // we eliminated duplicates in-place in contentsArray