code: private void addSupertypeEdges(ClassVertex vertex, LinkedList<XClass> workList) {
          XClass xclass = vertex.getXClass();
  
          // Direct superclass
          ClassDescriptor superclassDescriptor = xclass.getSuperclassDescriptor();
          if (superclassDescriptor != null) {
              addInheritanceEdge(vertex, superclassDescriptor, false, workList);
          }
  
          // Directly implemented interfaces
          for (ClassDescriptor ifaceDesc : xclass.getInterfaceDescriptorList()) {
              addInheritanceEdge(vertex, ifaceDesc, true, workList);
          }
      }
docs: Add supertype edges to the InheritanceGraph for given ClassVertex. If any
  direct supertypes have not been processed, add them to the worklist.
  
  @param vertex
  a ClassVertex whose supertype edges need to be added
  @param workList
  work list of ClassVertexes that need to have their supertype
  edges added