Can DataNucleus persist an abstract base class parameterized with Generics?
===

Using DataNucleus, I have been happy using an abstract base class to provide a 'long' ID to the sub-classes (please note the primitive type).

When adapting an [example from JPA](http://aurelavramescu.blogspot.com/2011/04/jpa-with-google-guice.html) I got the idea to parameterize the base class. The purpose was to support different ID types, such as String.

    @PersistenceCapable
    @Inheritance(strategy=InheritanceStrategy.SUBCLASS_TABLE)
    @Version(strategy=VersionStrategy.VERSION_NUMBER, column="jdo_version")
    public abstract class VersionedIdEntity<P>
        implements Serializable {

      static final long serialVersionUID = 1L;

      @PrimaryKey
      @Persistent(valueStrategy=IdGeneratorStrategy.INCREMENT)
      private P id;
		
      public P getId() {
        return id;
      }
    }


Generics made me use the wrapped Java type 'Long', so sub-classes were declared like this:

    public class Account extends VersionedIdEntity<Long>

My switch to the new base class caused an error stating that no implementation for 'java.lang.Object' was found.

> org.datanucleus.exceptions.NucleusUserException: Field "VersionedIdEntity.id" is declared as a reference type (interface/Object) but no implementation classes of "java.lang.Object" have been found!

Is the error related to type erasure?

Additional questions would be (1) how JPA deals with it and (2) whether I can restrict the type P to [types persistable in DataNucleus](http://www.datanucleus.org/products/datanucleus/jdo/types.html), such as:

    <? extends PersistableType>

While I could not find help elsewhere, the question could have been asked before. In that event, a brief pointer would be much appreciated.
