if (document.treeLevel[nextNode] > level) {
if (nextNode < document.size && document.treeLevel[nextNode] > level) {
	public Node getFirstChild() {		short level = document.treeLevel[nodeNumber];		int nextNode = nodeNumber + 1;		if (document.treeLevel[nextNode] > level) {			return document.getNode(nextNode);		} else			return null;	}