node = node.succ();
      }
    } else {
      node = header.succ();
    }
    return (node == header || !range.contains(node.getElement())) ? null : node;
  }

  private @Nullable AvlNode<E> lastNode() {
    AvlNode<E> root = rootReference.get();
    if (root == null) {
      return null;
    }
    AvlNode<E> node;
    if (range.hasUpperBound()) {

        private static final String PRIORITY_ELEMENT = "priority";

        private static final String CHANGEFREQ_ELEMENT = "changefreq";

        private static final String LASTMOD_ELEMENT = "lastmod";

        private static final String LOC_ELEMENT = "loc";

        private static final String URL_ELEMENT = "url";

        private SitemapSet sitemapSet;

        private SitemapUrl sitemapUrl;