Bug-Fix when super-class is Audited-Entity

java.lang.NullPointerException
	at org.hibernate.envers.internal.entities.mapper.relation.ToOneIdMapper.nullSafeMapToEntityFromMap(ToOneIdMapper.java:110)
	at org.hibernate.envers.internal.entities.mapper.relation.AbstractToOneMapper.mapToEntityFromMap(AbstractToOneMapper.java:67)
	at org.hibernate.envers.internal.entities.mapper.MultiPropertyMapper.mapToEntityFromMap(MultiPropertyMapper.java:172)
	at org.hibernate.envers.internal.entities.mapper.SubclassPropertyMapper.mapToEntityFromMap(SubclassPropertyMapper.java:102)
	at org.hibernate.envers.internal.entities.mapper.SubclassPropertyMapper.mapToEntityFromMap(SubclassPropertyMapper.java:102)
	at org.hibernate.envers.internal.entities.EntityInstantiator.createInstanceFromVersionsEntity(EntityInstantiator.java:113)
	at org.hibernate.envers.internal.entities.EntityInstantiator.addInstancesFromVersionsEntities(EntityInstantiator.java:174)
	at org.hibernate.envers.query.internal.impl.EntitiesAtRevisionQuery.list(EntitiesAtRevisionQuery.java:136)
	at org.hibernate.envers.query.internal.impl.AbstractAuditQuery.getSingleResult(AbstractAuditQuery.java:113)
	at org.hibernate.envers.internal.reader.AuditReaderImpl.find(AuditReaderImpl.java:138)
	at org.hibernate.envers.internal.reader.AuditReaderImpl.find(AuditReaderImpl.java:108)
	at org.hibernate.envers.internal.reader.AuditReaderImpl.find(AuditReaderImpl.java:102)