public Iterable<JvmClass> allDirectSupertypes(JvmClass cls) {
    // return only those direct supertypes that exist in the graph as Nodes
    return flat(map(cls.getSuperTypes(), st -> getNodes(new JvmNodeReferenceID(st), JvmClass.class)));
  }
public Iterable<JvmClass> allDirectSupertypes(JvmClass cls)