RelationService.addRelationType (and RelationServiceMBean.addRelationType) should be explicitly specified to throw IllegalArgumentException if the RelationType argument returns null from its getRelationTypeName(). The other RelationService methods that take a relation type name are all spec'd to reject a null name. Thus if addRelationType allows one, you end up with a RelationType that you can do nothing with. In particular, you can't even remove it again.