private static void writeRoots(
Element element, Collection<TreeItem<Pair<AbstractUrl, String>>> roots) {
for (TreeItem<Pair<AbstractUrl, String>> root : roots) {
final AbstractUrl url = root.getData().getFirst();
if (url == null) continue;
final Element list = new Element(FAVORITES_ROOT);
url.write(list);
list.setAttribute(CLASS_NAME, root.getData().getSecond());
element.addContent(list);
final List<TreeItem<Pair<AbstractUrl, String>>> children = root.getChildren();
if (children != null && !children.isEmpty()) {
writeRoots(list, children);
}
}
}
