@Entity
public class Event {
    @Id
    @GeneratedValue
    private Long id;

    public Long getId() {
        return id;
    }
}

@MappedSuperclass
public abstract class AbstractBase {
    @OneToOne
    @JoinColumn(name = "MYEVENT")
    private Event event;
}

@Entity
@AssociationOverride(name = "event", foreignKey = @ForeignKey(name = "FK_REAL_EVENT"))
public class RealClass extends AbstractBase {
}

Caused by: java.lang.NullPointerException
	at org.hibernate.cfg.annotations.TableBinder.buildAndFillTable(TableBinder.java:512)
	at org.hibernate.cfg.annotations.EntityBinder.addJoin(EntityBinder.java:968)
	at org.hibernate.cfg.annotations.EntityBinder.addJoin(EntityBinder.java:879)
	at org.hibernate.cfg.ClassPropertyHolder.addJoin(ClassPropertyHolder.java:207)
	at org.hibernate.cfg.AnnotationBinder.processElementAnnotations(AnnotationBinder.java:1815)
	at org.hibernate.cfg.AnnotationBinder.processIdPropertiesIfNotAlready(AnnotationBinder.java:925)
	at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:752)
	at org.hibernate.boot.model.source.internal.annotations.AnnotationMetadataSourceProcessorImpl.processEntityHierarchies(AnnotationMetadataSourceProcessorImpl.java:249)
	at org.hibernate.boot.model.process.spi.MetadataBuildingProcess$1.processEntityHierarchies(MetadataBuildingProcess.java:222)
	at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:265)
	at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build(MetadataBuildingProcess.java:83)
	at org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:418)
	at org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:87)
	at org.hibernate.boot.MetadataSources.buildMetadata(MetadataSources.java:179)

@Entity
@AssociationOverride(name = "event", joinColumns = @JoinColumn(name = "MYEVENT"), foreignKey = @ForeignKey(name = "FK_REAL_EVENT"))
public class RealClass extends AbstractBase {
}