code: protected Entry<E> standardPollLastEntry() {
      Iterator<Entry<E>> entryIterator = descendingMultiset().entrySet().iterator();
      if (!entryIterator.hasNext()) {
        return null;
      }
      Entry<E> entry = entryIterator.next();
      entry = Multisets.immutableEntry(entry.getElement(), entry.getCount());
      entryIterator.remove();
      return entry;
    }
docs: A sensible definition of {@link #pollLastEntry()} in terms of {@code
  descendingMultiset().entrySet().iterator()}.
  
  <p>If you override {@link #descendingMultiset()} or {@link #entrySet()}, you may wish to
  override {@link #pollLastEntry()} to forward to this implementation.