code: public E pollLast() {
          final Node<E> l = last;
          return (l == null) ? null : unlinkLast(l);
      }
docs: Retrieves and removes the last element of this list,
  or returns {@code null} if this list is empty.
  
  @return the last element of this list, or {@code null} if
  this list is empty
  @since 1.6