anchor.diff:      return result ?? supertypes;
     }
   
  -  void addInterface(List<Supertype> interfaces, List<Supertype> superclasses,
  -      Supertype type) {
  +  void addInterface(Map<Class, Supertype> interfaces,
  +      List<Supertype> superclasses, Supertype type) {
       // ignore: unnecessary_null_comparison
       if (type == null) return null;
       if (!classBuilder.library.isNonNullableByDefault) {
  
positive.code:             }
            }
          }
          // ignore: unnecessary_null_comparison
        } else if (superclassInterfaces != null &&
            !classBuilder.library.isNonNullableByDefault &&
            supernode.classBuilder.library.isNonNullableByDefault) {
          interfaces = <Supertype>[];
          for (int i = 0; i < superclassInterfaces.length; i++) {
            addInterface(interfaces, superclasses, superclassInterfaces[i]);
          }
        } else {
          interfaces = superclassInterfaces;
        }
      }
  
  
negative.code:       recordSupertype(superclass);
      }
      // ignore: unnecessary_null_comparison
      if (interfacesList != null) {
        for (Supertype superinterface in interfacesList) {
          recordSupertype(superinterface);
        }
      }
  