一开始报错如下：

Cannot read properties of null (reading 'forEach')`

原因是返回的属性分组没有关联属性，即attrs: null，所以遍历失败
评论区说可以在前端检查，我试了一下还是报错如下

"TypeError: Cannot read properties of undefined (reading 'attrId')"

前端真的头大，折腾半天最后还是在后端检查null才成功

//2、查询所有属性
return attrGroupEntities.stream().map(group -> {AttrGroupWithAttrsVo attrsVo = new AttrGroupWithAttrsVo();BeanUtils.copyProperties(group, attrsVo);List<AttrEntity> attrs = attrService.getRelationAttr(attrsVo.getAttrGroupId());attrsVo.setAttrs(attrs);return attrsVo;
}).filter(item -> item.getAttrs() != null).collect(Collectors.toList());