anchor.diff:    factory TypeParameterBuilder() = _$TypeParameterBuilder;
   }
   
  -abstract class Property extends NamedElement
  -    implements Built<Property, PropertyBuilder> {
  +abstract class Property
  +    implements Built<Property, PropertyBuilder>, NamedElement {
     static final Serializer<Property> serializer = _$propertySerializer;
     String get name;
     Classifier get type;
  
positive.code: }
  
  abstract class TypeParameter
      implements NamedElement, Built<TypeParameter, TypeParameterBuilder> {
    static final Serializer<TypeParameter> serializer = _$typeParameterSerializer;
    String get name;
    @nullable
  
negative.code:   factory PropertyBuilder() = _$PropertyBuilder;
  }
  
  abstract class ValueClass
      implements Built<ValueClass, ValueClassBuilder>, GenericClassifier {
    static final Serializer<ValueClass> serializer = _$valueClassSerializer;
    String get name;
    BuiltSet<TypeParameter> get genericTypes;
  