@javax.persistence.Entity
@DiscriminatorValue("ArticleBook")
public class ArticleBook extends AbstractArticle implements java.io.Serializable {

....
        @ManyToOne
	public Book getBook() {
		return book;
	}

	public void setBook(Book book) {
		this.book = book;
	}
...

@javax.persistence.Entity
@Table(name = "acc_article")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@Multitenant( value=MultitenantType.TABLE_PER_TENANT)
public abstract class AbstractArticle extends BasePropertyChangeSupport implements java.io.Serializable,DeletableEntity {

Caused by: java.lang.NullPointerException
	at org.eclipse.persistence.mappings.ForeignReferenceMapping.isLockableMapping(ForeignReferenceMapping.java:1000)
	at org.eclipse.persistence.descriptors.ClassDescriptor.postInitialize(ClassDescriptor.java:3613)
	at org.eclipse.persistence.descriptors.ClassDescriptor.postInitialize(ClassDescriptor.java:3583)
	at org.eclipse.persistence.internal.sessions.AbstractSession.updateTablePerTenantDescriptors(AbstractSession.java:1216)
	at org.eclipse.persistence.sessions.server.ClientSession.<init>(ClientSession.java:126)
	at org.eclipse.persistence.sessions.server.ServerSession.acquireClientSession(ServerSession.java:390)
	at org.eclipse.persistence.internal.jpa.EntityManagerImpl.getActivePersistenceContext(EntityManagerImpl.java:1714)
	at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.begin(EntityTransactionImpl.java:49)
	at org.springframework.orm.jpa.DefaultJpaDialect.beginTransaction(DefaultJpaDialect.java:70)
	at org.springframework.orm.jpa.JpaTransactionManager.doBegin(JpaTransactionManager.java:332)