Turns out this issue may be a duplicate of a known issue, taking this over to the dev list. org/hibernate/test/annotations/cid/CompositeIdIdentityTest.java: 7 package org.hibernate.test.annotations.cid; 48 @RequiresDialectFeature(DialectChecks.SupportsIdentityColumns.class) 49 @TestForIssue( jiraKey = "HHH-9662" ) 50 public class CompositeIdIdentityTest extends BaseCoreFunctionalTestCase { 51 52 @Test 53 @FailureExpected( jiraKey = "HHH-9662" ) 54 public void testCompositePkWithIdentity() throws Exception { 55 doInHibernate( this::sessionFactory, session -> { 56 Animal animal = new Animal(); 57 animal.setSubId( 123L ); 58 session.persist(animal); 59 } ); 60 } 61 70 @Entity 71 @Table(name = "animal") 72 @IdClass(IdWithSubId.class) 73 public static class Animal { 74 75 @Id 76 @GeneratedValue(strategy = GenerationType.IDENTITY) 77 private Long id; 78 79 @Id 80 @Column(name = "sub_id") 81 private Long subId; 82 From: Jason Pyeron [mailto:jpyeron@pdinc.us] Sent: Tuesday, April 21, 2020 1:32 AM To: &#39;hibernate-users(a)lists.jboss.org&#39; <hibernate-users(a)lists.jboss.org&gt; Subject: HHH-6044 and partial identifier generation - No part of a composite identifier may be null HibernateException [note this is an issue with sequences too] Quoting https://docs.jboss.org/hibernate/orm/5.4/userguide/html_single/Hibernate_... With non-aggregated composite identifiers, Hibernate also supports "partial" generation of the composite values. Example 135. @IdClass with partial identifier generation using @GeneratedValue I seem to be having the same issues as https://hibernate.atlassian.net/browse/HHH-6044 I have existing tables / Entities (simplified): CREATE TABLE [cresaptown].[saar]( [id] [bigint] IDENTITY(1,1) NOT NULL primary key ); @Entity @Table(schema = "cresaptown", name = "saar") public class SystemAccessAuthorizationRequest { @Id @GeneratedValue Long id; } CREATE TABLE [cresaptown].[signature]( [rid] [bigint] IDENTITY(1,1) NOT NULL, [sid] [bigint] NOT NULL, PRIMARY KEY ([rid],[sid]), FOREIGN KEY([rid]) REFERENCES [cresaptown].[saar] ([id]) ); @Entity @Table(schema = "cresaptown", name = "signature") @IdClass(Signature.ID.class) public class Signature { @Id @Column(name = "sid") @GeneratedValue Long sid; @Id @JoinColumn(name = "rid") @ManyToOne SystemAccessAuthorizationRequest rid; public static class ID implements Serializable { Long sid; Long rid; } } A code fragment em.getTransaction().begin(); SystemAccessAuthorizationRequest saar = new SystemAccessAuthorizationRequest(); em.persist(saar); Signature sig = new Signature(); sig.setRid(saar); em.persist(sig); em.getTransaction().commit(); gives this exception, but if I disable the null check in AbstractEntityTuplizer.getIdentifier, I get the same issue as in HHH-6044 javax.persistence.PersistenceException: org.hibernate.HibernateException: No part of a composite identifier may be null at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:154) at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:181) at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:188) at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:716) at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:696) at x.Testclass.x(Testclass.java:38) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:89) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209) Caused by: org.hibernate.HibernateException: No part of a composite identifier may be null at org.hibernate.tuple.entity.AbstractEntityTuplizer$IncrediblySillyJpaMapsIdMappedIdentifierValueMarshaller.getIdentifier(AbstractEntityTuplizer.java:365) at org.hibernate.tuple.entity.AbstractEntityTuplizer.getIdentifier(AbstractEntityTuplizer.java:219) at org.hibernate.persister.entity.AbstractEntityPersister.getIdentifier(AbstractEntityPersister.java:5119) at org.hibernate.persister.entity.AbstractEntityPersister.isTransient(AbstractEntityPersister.java:4819) at org.hibernate.engine.internal.ForeignKeys.isTransient(ForeignKeys.java:294) at org.hibernate.event.internal.EntityState.getEntityState(EntityState.java:59) at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:95) at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:55) at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:102) at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:710) ... 25 more