toJSON时无法将null放进JSONObject的处理方式
SerializeConfig serializeConfig=new SerializeConfig();
serializeConfig.config(AnswerRuleCollections.class, SerializerFeature.WriteMapNullValue,true);
JSON.toJSON(cleanDataOrSynonym,serializeConfig)

toJSONString时无法将null放进String的处理方式
JSON.toJSONString(sourceObject, SerializerFeature.WriteMapNullValue)