Minor Description
If a property is set with a null value in the Entity.createEntityManagerFactory, a NullPointerException is thrown due to PersistenceUnitInfoImpl's use of Properties for the _props field (which extends Hashtable which doesn't allow nulls). Although not specifically laid out by the API, it accepts Map, which is incompatible with Properties/Hashtable in this instance. HashMap would be the preffered type here.
Currently this was working with EclipseLink, as I set some properties to null to override defaults set in the persistence.xml file based on some dynamic criteria.