EDIT

...Dazu wollte ich zunächst eine neue Referenz erstellen.
Neues Autorenteam mit einem neu erstellten Autor, hatte beim 2. Autor „OK“ vergessen, siehe ScreenShot 1
Beim Speichern:

...
...

Caused by: org.hibernate.exception.ConstraintViolationException: could not execute statement
               at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:59)
               at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
               at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:109)
               at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:95)
               at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:207)
               at org.hibernate.engine.jdbc.batch.internal.NonBatchingBatch.addToBatch(NonBatchingBatch.java:45)
               at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2886)
               at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3386)
               at org.hibernate.action.internal.EntityInsertAction.execute(EntityInsertAction.java:89)
               at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:560)
               at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:434)
               at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:337)
               at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:39)
               at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1282)
               at org.hibernate.envers.internal.synchronization.AuditProcess.doBeforeTransactionCompletion(AuditProcess.java:156)
               at org.hibernate.envers.internal.synchronization.AuditProcessManager$1.doBeforeTransactionCompletion(AuditProcessManager.java:46)
               at org.hibernate.engine.spi.ActionQueue$BeforeTransactionCompletionProcessQueue.beforeTransactionCompletion(ActionQueue.java:899)
               at org.hibernate.engine.spi.ActionQueue.beforeTransactionCompletion(ActionQueue.java:481)
               at org.hibernate.internal.SessionImpl.beforeTransactionCompletion(SessionImpl.java:2340)
               at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.beforeTransactionCompletion(JdbcCoordinatorImpl.java:485)
               at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.beforeCompletionCallback(JdbcResourceLocalTransactionCoordinatorImpl.java:147)
               at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.access$100(JdbcResourceLocalTransactionCoordinatorImpl.java:38)
               at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.commit(JdbcResourceLocalTransactionCoordinatorImpl.java:231)
               at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:65)
               at org.springframework.orm.hibernate5.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:581)
               ... 100 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'teamMembers_id' cannot be null
               at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
               at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
               at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
               at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
               at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
               at com.mysql.jdbc.Util.getInstance(Util.java:387)
               at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:932)
               at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3878)
               at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3814)
               at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2478)
               at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2625)
               at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2551)
               at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1861)
               at com.mysql.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2073)
               at com.mysql.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2009)
               at com.mysql.jdbc.PreparedStatement.executeLargeUpdate(PreparedStatement.java:5094)
               at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1994)
               at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeUpdate(NewProxyPreparedStatement.java:384)
               at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:204)
               ... 120 more