Amendment

[janvanmansum]

As discussed with @qqmyers changing DatasetFieldType.isControlledVocabulary() to return allowControlledVocabulary instead of accessing the database to see if the list of terms is non-empty. This gets rid of NPE's in EclipseLink's AbstractSession.executeDeferredEvents, e.g.,

  java.lang.NullPointerException
        at org.eclipse.persistence.internal.sessions.AbstractSession.executeDeferredEvents(AbstractSession.java:1534)
        at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.internalExecuteQuery(UnitOfWorkImpl.java:3005)
        at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1898)
        at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1880)

which are presumably caused by using the EntityManager from a thread that is not supposed to use it. See also: https://stackoverflow.com/questions/73974404/npe-in-eclipse-link-abstractsession-executedeferredeventsabstractsession-java1