private List<T_TREE_NODE> getEmptyList() {
        if (emptyList == null) {
            emptyList = new ArrayList<>();
        }
        return emptyList;
    }
Creates a new instance with a given node as the root

@param root the node to be used as the root.
stroom-core-client-widget/src/main/java/stroom/widget/htree/client/treelayout/util/DefaultTreeForTreeLayout.java