IllegalArgumentException when use ZkUtil::listSubTreeBFS to list "/"

java.lang.IllegalArgumentException: Invalid path string "//a_test" caused by empty node name specified @1

public static List<String> listSubTreeBFS(
        ZooKeeper zk,
        final String pathRoot) throws KeeperException, InterruptedException {
    Queue<String> queue = new ArrayDeque<>();
    List<String> tree = new ArrayList<>();
    queue.add(pathRoot);
    tree.add(pathRoot);
    while (!queue.isEmpty()) {
        String node = queue.poll();
        List<String> children = zk.getChildren(node, false);
        for (final String child : children) {
            // Fix "//some_path" bugs when list "/"                
            final String childPath = (node.equals("/") ? "" : node) + "/" + child;
            queue.add(childPath);
            tree.add(childPath);
        }
    }
    return tree;
}