缓存： Null key returned for cache operation (maybe you are using named params on classes without debug

 错误：

Null key returned for cache operation (maybe you are using named params on classes without debug info?) Builder[public java.lang.String com.gwm.service.impl.TestService.selectById(java.io.Serializable)] caches=[hour] | key='#id' | keyGenerator='' | cacheManager='' | cacheResolver='' | condition='' | unless='' | sync='false'

 调用方法：

 @Cacheable(value = "hour", key = "#id")
public String selectById(Serializable id) {
    Long timestamp = System.currentTimeMillis();
         return timestamp.toString();

出错原因：  key中的id 没有传值，在调用方法时，不能传null值。

eg：

             Serializable id = "aa";
   String meg=testService.selectById(id);   传上值！！！！！