code: void link(Node<K, V> sentinel, Node<K, V> node) {
      node.setPreviousInVariableOrder(sentinel.getPreviousInVariableOrder());
      node.setNextInVariableOrder(sentinel);
  
      sentinel.getPreviousInVariableOrder().setNextInVariableOrder(node);
      sentinel.setPreviousInVariableOrder(node);
    }
docs: Adds the entry at the tail of the bucket's list.