}

    @Override
    @ParametricNullness
    public E first() {
      return getElementOrThrow(multiset().firstEntry());
    }

    @Override
    @ParametricNullness
    public E last() {
      return getElementOrThrow(multiset().lastEntry());
    }
  }

  /** A skeleton navigable implementation for {@link SortedMultiset#elementSet}. */