空map和list判斷，且將null填充成想要展現的0

public Map<String, Object> selectDataNumRank(Map<String, Object> map) {
        Map<String,Object> resultMap = new HashMap<>();
        List<Map<String,Object>> list = policeStationCheckMapper.selectDataNumRank(map);

        if(null == list || list.isEmpty()){
            System.out.println("空的");
            Map<String,Object> fMap = new HashMap<>();
            fMap.put("num",0);
            fMap.put("rank",0);
            list.add(fMap);
        }

        resultMap.put("list",list);
        resultMap.put("status",200);
        return resultMap;
    }

兩段判斷爲空，list不存在或者無內容

null==list，null要在前，不然空指針異常