I used hibernate.transform_hbm_xml.enabled to convert a legacy .hbm.xml to the modern format and then tried to dump it as XML to standard output.

I used org.glassfish.jaxb:jaxb-runtime:4.0.2

JaxbEntityMappings obj = ...
jaxbContext = JAXBContext.newInstance(JaxbEntityMappings.class);
final Marshaller marshaller = jaxbContext.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
marshaller.marshal(obj, System.out);

Got this error:

noformat
Caused by: java.lang.NullPointerException
at org.hibernate.boot.jaxb.mapping.marshall.AccessTypeMarshalling.toXml(AccessTypeMarshalling.java:22)
at org.hibernate.boot.jaxb.mapping.Adapter1.marshal(Adapter1.java:17)
at org.hibernate.boot.jaxb.mapping.Adapter1.marshal(Adapter1.java:7)
at org.glassfish.jaxb.runtime.v2.runtime.reflect.AdaptedAccessor.get(AdaptedAccessor.java:46)
... 23 more
noformat

Same problem with the class FetchTypeMarshalling

I think a null check is needed in toXml()