JSON.toJSONString(outPutFeeds, SerializerFeature.WriteMapNullValue)
| WriteMapNullValue | 是否输出值为null的字段,默认为false | 
JSON.toJSONString(outPutFeeds, SerializerFeature.WriteMapNullValue)
| WriteMapNullValue | 是否输出值为null的字段,默认为false | 
JSON.toJSONString(outPutFeeds, SerializerFeature.WriteMapNullValue)
