I didn't see GenerationType.AUTO described in the Hibernate manual, but according to https://docs.jboss.org/author/display/AS71/JPA+Reference+Guide#JPAReferenceGuide-Persistenceunitproperties,

In Hibernate 4.x, if new_generator_mappings is true:

• @GeneratedValue(AUTO) maps to org.hibernate.id.enhanced.SequenceStyleGenerator
• @GeneratedValue(TABLE) maps to org.hibernate.id.enhanced.TableGenerator
• @GeneratedValue(SEQUENCE) maps to org.hibernate.id.enhanced.SequenceStyleGenerator

In Hibernate 4.x, if new_generator_mappings is false:

• @GeneratedValue(AUTO) maps to Hibernate "native"
• @GeneratedValue(TABLE) maps to org.hibernate.id.MultipleHiLoPerTableGenerator
• @GeneratedValue(SEQUENCE) to Hibernate "seqhilo"

Currently, the IdGenerator is not being bound properly.

org.hibernate.metamodel.internal.source.annotations.attribute.SimpleIdentifierSourceImpl.getIdentifierGeneratorDescriptor() returns null.