org.hibernate.type.Type extends Serializable. org.hibernate.persister.entity.DiscriminatorType includes a field "private final Loadable persister" that is not serializable.
As a result my 2nd level cache cannot serialize a org.hibernate.cache.spi.QueryKey due to one of the named parameters being a DiscriminatorType. Since DiscriminatorType is marked as Serializable, it should be Serializable.