java.lang.UnsupportedOperationException: null

    public void addAllToChild(List<DocTreeVo> list) {
        if (CollectionUtils.isEmpty(list)) {
            return;
        }
        if (childList == null) {
            childList = new ArrayList<>();
        }
        childList.addAll(list);
    }

    private List<DocTreeVo> keepOnlyColoredNodes(List<DocTreeVo> nodeList) {
        if (CollectionUtils.isEmpty(nodeList)) {
            return ListUtils.EMPTY_LIST;
        }
        List<DocTreeVo> newRootList = nodeList.stream().filter(item -> item.getColor() == 1)
                .collect(Collectors.toList());
        for (DocTreeVo vo : newRootList) {
            vo.setChildList(keepOnlyColoredNodes(vo.getChildList()));
        }
        return newRootList;
    }