Spring Cache doesn't ignore Null key even I set the condition

In my application, the cache key is nullable, so I just wanna put it in cache when the key is not null.

I've tried a lot of different ways but it looks like Spring Cache always want a none empty key. Otherwise it throws Exception:

IllegalArgumentException: Null key returned for cache operation (maybe you are using named params on classes without debug info?) Builder[public com.madme.sharding.model.App com.madme.sharding.service.impl.AppServiceImpl.saveOrUpdateApp(com.madme.sharding.model.App)] caches=[appsCache] | key='#result.uuid' | keyGenerator='' | cacheManager='redisCacheManager' | cacheResolver='' | condition='' | unless='#p0.uuid == null' Ref: 1490185514616_gcfal96

I thought if I specified 'unless' condition like below, it should just ignore this CachePut without throwing any exceptions.

// I've tried #result.uuid and #p0.uuid, same output@CachePut(value = APPS_CACHE, cacheManager = "redisCacheManager", key = "#result.uuid", unless = "#result.uuid == null")public App saveOrUpdateApp(App app) {    return appRepository.saveAndFlush(app);}

Any one has any ideas?

Thanks in advance.