[pardon the top post, it did not mix in well] It looks like [stack trace 1] the option is never set in this situation, because the only place it is set is when if ( trueOneToOne || mapToPK || !BinderHelper.isEmptyAnnotationValue( mappedBy ) ) { but since there is a FK involved it is running //has a FK on the table bindManyToOne( cascadeStrategy, joinColumns, optional, ignoreNotFound, cascadeOnDelete, targetEntity, propertyHolder, inferredData, true, isIdentifierMapper, inSecondPass, propertyBinder, context ); Debugging shows the optional==true. Looking at that method, the only use of optional parameter is if ( !optional ) { for ( Ejb3JoinColumn column : columns ) { column.setNullable( false ); } } Which is not relevant, since optional is true. That is the last line of code in bindOneToOne(...) Now when the evaluation of the properties are being made to persist in the EntityMetamodel [stack trace 2] the optional is false. As a consequence the checkNullability(...) will fail with a PropertyValueException during the nullability check [stack trace 3]: if ( !nullability[i] && value == null ) { //check basic level one nullablilty throw new PropertyValueException( "not-null property references a null or transient value", persister.getEntityName(), persister.getPropertyNames()[i] ); } 1: AnnotationBinder.bindManyToOne(String, Ejb3JoinColumn[], boolean, boolean, boolean, XClass, PropertyHolder, PropertyData, boolean, boolean, boolean, PropertyBinder, MetadataBuildingContext) line: 3116 AnnotationBinder.bindOneToOne(String, Ejb3JoinColumn[], boolean, FetchMode, boolean, boolean, XClass, PropertyHolder, PropertyData, String, boolean, boolean, boolean, PropertyBinder, MetadataBuildingContext) line: 3243 AnnotationBinder.processElementAnnotations(PropertyHolder, Nullability, PropertyData, HashMap<String,IdentifierGeneratorDefinition>, EntityBinder, boolean, boolean, boolean, MetadataBuildingContext, Map<XClass,InheritanceState>) line: 1844 AnnotationBinder.processIdPropertiesIfNotAlready(Map<XClass,InheritanceState>, MetadataBuildingContext, PersistentClass, EntityBinder, PropertyHolder, HashMap<String,IdentifierGeneratorDefinition>, ElementsToProcess, boolean, Set<String>) line: 975 AnnotationBinder.bindClass(XClass, Map<XClass,InheritanceState>, MetadataBuildingContext) line: 802 AnnotationMetadataSourceProcessorImpl.processEntityHierarchies(Set<String>) line: 254 MetadataBuildingProcess$1.processEntityHierarchies(Set<String>) line: 230 MetadataBuildingProcess.complete(ManagedResources, BootstrapContext, MetadataBuildingOptions) line: 273 EntityManagerFactoryBuilderImpl.metadata() line: 1214 EntityManagerFactoryBuilderImpl.build() line: 1245 HibernatePersistenceProvider.createEntityManagerFactory(String, Map) line: 56 Persistence.createEntityManagerFactory(String, Map) line: 79 Persistence.createEntityManagerFactory(String) line: 54 JPAUnitTestCase.init() line: 27 2: PropertyFactory.buildEntityBasedAttribute(EntityPersister, SessionFactoryImplementor, int, Property, boolean) line: 158 EntityMetamodel.<init>(PersistentClass, EntityPersister, SessionFactoryImplementor) line: 224 SingleTableEntityPersister(AbstractEntityPersister).<init>(PersistentClass, EntityDataAccess, NaturalIdDataAccess, PersisterCreationContext) line: 601 SingleTableEntityPersister.<init>(PersistentClass, EntityDataAccess, NaturalIdDataAccess, PersisterCreationContext) line: 125 NativeConstructorAccessorImpl.newInstance0(Constructor<?>, Object[]) line: not available [native method] NativeConstructorAccessorImpl.newInstance(Object[]) line: not available DelegatingConstructorAccessorImpl.newInstance(Object[]) line: not available Constructor<T>.newInstance(Object...) line: not available PersisterFactoryImpl.createEntityPersister(Class<EntityPersister>, PersistentClass, EntityDataAccess, NaturalIdDataAccess, PersisterCreationContext) line: 96 PersisterFactoryImpl.createEntityPersister(PersistentClass, EntityDataAccess, NaturalIdDataAccess, PersisterCreationContext) line: 77 MetamodelImpl.initialize(MetadataImplementor, JpaMetaModelPopulationSetting) line: 181 SessionFactoryImpl.<init>(MetadataImplementor, SessionFactoryOptions) line: 299 SessionFactoryBuilderImpl.build() line: 468 EntityManagerFactoryBuilderImpl.build() line: 1249 HibernatePersistenceProvider.createEntityManagerFactory(String, Map) line: 56 Persistence.createEntityManagerFactory(String, Map) line: 79 Persistence.createEntityManagerFactory(String) line: 54 JPAUnitTestCase.init() line: 27 3: Nullability.checkNullability(Object[], EntityPersister, Nullability$NullabilityCheckType) line: 92 Nullability.checkNullability(Object[], EntityPersister, boolean) line: 55 EntityIdentityInsertAction(AbstractEntityInsertAction).nullifyTransientReferencesIfNotAlready() line: 116 EntityIdentityInsertAction(AbstractEntityInsertAction).makeEntityManaged() line: 125 ActionQueue.addResolvedEntityInsertAction(AbstractEntityInsertAction) line: 289 ActionQueue.addInsertAction(AbstractEntityInsertAction) line: 263 ActionQueue.addAction(EntityIdentityInsertAction) line: 317 DefaultPersistEventListener(AbstractSaveEventListener).addInsertAction(Object[], Serializable, Object, EntityPersister, boolean, EventSource, boolean) line: 330 DefaultPersistEventListener(AbstractSaveEventListener).performSaveOrReplicate(Object, EntityKey, EntityPersister, boolean, Object, EventSource, boolean) line: 287 DefaultPersistEventListener(AbstractSaveEventListener).performSave(Object, Serializable, EntityPersister, boolean, Object, EventSource, boolean) line: 193 DefaultPersistEventListener(AbstractSaveEventListener).saveWithGeneratedId(Object, String, Object, EventSource, boolean) line: 123 DefaultPersistEventListener.entityIsTransient(PersistEvent, Map) line: 185 DefaultPersistEventListener.onPersist(PersistEvent, Map) line: 128 DefaultPersistEventListener.onPersist(PersistEvent) line: 55 1021082377.accept(Object, Object) line: not available EventListenerGroupImpl<T>.fireEventOnEachListener(U, BiConsumer<T,U>) line: 102 SessionImpl.firePersist(PersistEvent) line: 710 SessionImpl.persist(Object) line: 696 JPAUnitTestCase.hhh13959TestProfile() line: 43