Hi Paata,
It is not possible to tell the engine explicitly to treat a value as a JPA variable. So in the session you debugged, both the JPA serializer and the Java object serializer were considered for serialization. If you don’t implement java.io.Serializable in your entity class, then the second one will not be considered and the JPA serializer should be used by default. The workaround you found (changing the default serialization format) does work and is probably fine, but rather hacky.
Cheers,
Thorben