public Node add(String name) {
            if (children.containsKey(name)) return children.get(name);

            Node child = new Node(this, name);
            children.put(name, child);
            return child;
        }
Adds an empty node to this and returns it. If it already exists this does nothing but return the node
zkfacade/src/main/java/com/yahoo/vespa/curator/mock/MemoryFileSystem.java