docs: private void unlink(E e) {
          final E prev = e.getPrevious();
          final E next = e.getNext();
  
          if (prev == null) {
              first = next;
          } else {
              prev.setNext(next);
              e.setPrevious(null);
          }
  
          if (next == null) {
              last = prev;
          } else {
              next.setPrevious(prev);
              e.setNext(null);
          }
      }