查询任务桌面失败

出现一个问题：

private List<Map<String, Object>> getBuIdByTask(Long userId, Integer clientShow) throws Exception {
        int complete_status = TaskCenterDefinedCode.OPERATION_STATUS.COMPLETE.getNumberCode().intValue();
        // 默认手机端 0，1
        List<Long> cardTypeUkids = getActionUkidsForTaskTags(clientShow, null);
        TsOperationDOExample tsOperationDOExample = new TsOperationDOExample();
        List<String> fields = new ArrayList<>(1);
        fields.add("owner_id");
      //  fields.add("operation_ukid");  //新加入 ①
        tsOperationDOExample.setCustomFields(fields);
        tsOperationDOExample.createCriteria().andStatusLessThan(complete_status)
                .andOpUserIdEqualTo(userId)
                .andOperationUnitUkidIn(cardTypeUkids);
        List<TsOperation> tsOperations = tsOperationManager.selectByExample(tsOperationDOExample);
        List<Map<String, Object>> buMaps = new ArrayList<>();
        Set<Long> buIdSets = tsOperations.stream().map(TsOperation::getOwnerId).filter(ObjectUtil::isNotEmpty).collect(Collectors.toSet()); //这里报错②
        List<CmBusinessUnitInfo> businessUnits = cmBusinessUnitsService.getBusinessUnitInfoByBuIds(buIdSets);
        for (CmBusinessUnitInfo cmBusinessUnitInfo : businessUnits) {
            if (cmBusinessUnitInfo == null) {
                continue;
            }
            Map<String, Object> bu = new HashMap<>(2);
            bu.put("buId", cmBusinessUnitInfo.getBusinessUnitId());
            bu.put("buName", cmBusinessUnitInfo.getBusinessUnitName());
            buMaps.add(bu);
        }
        return buMaps;
    }

如果不新加入 ① fields.add("operation_ukid");

Set<Long> buIdSets = tsOperations.stream().map(TsOperation::getOwnerId).filter(ObjectUtil::isNotEmpty).collect(Collectors.toSet()); //这里报错②

经过查找，

tsOperationManager.selectByExample(tsOperationDOExample); 只会返回owner_id这个字段，并且使用

TsOperation返回。当owner_id为null时，TsOperation会为null。
所以这里把主键也返回，就不会返回null对象了。