code: protected Node<V> cleanNode(int bitNumber)
  	{
  		Node<V> node=cleanNodePath(bitNumber, config.layout, root);
  		if(node!=null)
  		{
  			Node<V> pre=node.getPre();
  			Node<V> next=node.getNext();
  			if(pre!=null)
  			{
  				pre.setNext(next);
  				node.setPre(null);
  			}else
  			{//设置头节点
  				firstAdd=next;
  			}
  			if(next!=null)
  			{
  				next.setPre(pre);
  				node.setNext(null);
  			}else
  			{//设置尾节点
  				lastAdd=pre;
  			}
  			size--;
  		}
  		return node;
  	}
docs: 清理节点
  @param bitNumber
  @return