集合为空时返回另一种方式而非null

之前代码：

  @GetMapping("checkContentList")
    @ResponseBodyMessage
    @ApiOperation(value = "获取列表信息")
    public List getList(@ApiParam(name = "filter", value = "过滤条件") @RequestParam(required = false) String filter,
                                               @ApiParam(name = "sort", value = "排序") @RequestParam(required = false) String sort) {
        List listData = service.list(sort, filter);
        if(listData.size()>0){
            List digchecks = listData.get(0).getDigchecks();
            Collections.sort(digchecks,(s1,s2)->s1.getContentCode().compareTo(s2.getContentCode()));
            return digchecks;
        }else{
          //这里换种方式      return  Collections.EMPTY_LIST  
            **return null;**
        }
    }

Collections 类提供了空集合常量对象，如Collections.EMPTY_LIST ，Collections.EMPTY_SET， Collections.EMPTY_MAP ，大家可以把return null 换成 return Collections.EMPTY_LIST,更优雅