when appendFields a Object with a Object attribute ,the whole project would not print any log。

when appendFields a Object with a Object attribute ,the whole project would not print any log。
- Version:logstash-logback-encoder：4.5.1
- Operating System:win10
- Config File (if you have sensitive info, please remove it):
- Sample Data:
- Steps to Reproduce:
`private final Logger logger = LoggerFactory.getLogger(getClass());`
`LogInfo logInfo = new LogInfo("",0);` _(LogInfo is my business Class, it can be any Class with a Object attribute_)
`logInfo.setRet(new Object());`
` logger.info(appendFields(logInfo),"access log");`