DataNucleus claims it support querying `@MappedSuperclass`, but their Criteria API implementation doesn't seem to support querying simple abstract `@Entity`.
In version 3.2.0, the code for `<X> Root<X> from(Class<X> cls)` includes the following line (197):
EntityType<X> entity = model.entity(cls);
In my understanding, it will only work with types registered as "EntityType"
The problem is that DataNucleus `MetamodelImpl` treats abstract entities as "MappedSuperclassType" instead of "EntityType", so I get the following exception when querying (with Spring Data JPA, btw):
Caused by: java.lang.IllegalArgumentException: Type <type> is not a known entity type