void Cellspace::makenull(TREE root) {
	if (root == -1)
		return;

	int id = nodes[root].get_leftmost_child();
	TNode node;
	if (id != -1) {
		node = nodes[id];
		makenull(id);
		id = node.get_right_sibling();
		while (id != -1) {
			makenull(id);
			node = nodes[id];
			id = node.get_right_sibling();
		}
	}
	node = nodes[root];
	node.set_label(NULL);
	node.set_parent(-1);
	node.set_leftmost_child(-1);
	node.set_right_sibling(-1);
}