bug description

Marshalling a JaxbHbmBasicAttributeType to xml throws a NPE if the generated attribut has not been set whereas the generated attribute of property-element is not declared as use="required" in the hibernate-mapping-4.0.xsd.

Step to reproduce

See attached test case

Workaround

explicitely set the generated attribute for JaxbHbmBasicAttributeType. It defaults to never, this value can be safely used.

Fix

handle a null argument in org.hibernate.boot.jaxb.hbm.internal.GenerationTimingConverter.toXml(GenerationTiming). See attached patch.