docs: private void initHeadTail(Node<E> h, Node<E> t) {
          if (h == t) {
              if (h == null)
                  h = t = new Node<>(null);
              else {
                  // Avoid edge case of a single Node with non-null item.
                  Node<E> newNode = new Node<>(null);
                  t.lazySetNext(newNode);
                  newNode.lazySetPrev(t);
                  t = newNode;
              }
          }
          head = h;
          tail = t;
      }