code: private Node<OWLClass> nodeToOwlClassNode(au.csiro.ontology.Node n) {
          if(n == null) return new OWLClassNode();
  
          final Set<OWLClass> classes = new HashSet<>();
  
          for (Object eq : n.getEquivalentConcepts()) {
              classes.add(getOWLClass(eq));
          }
  
          return new OWLClassNode(classes);
      }
docs: Transforms a {@link ClassNode} into a {@link Node} of {@link OWLClass}es.
  
  @param n may be null, in which case an empty Node is returned
  @return