anchor.diff:  abstract class ExternalClassBuilder
       implements Builder<ExternalClass, ExternalClassBuilder> {
     String name;
  -
     SetBuilder<TypeParameter> genericTypes = new SetBuilder<TypeParameter>();
   
     ExternalClassBuilder._();
  +
     factory ExternalClassBuilder() = _$ExternalClassBuilder;
   }
   
   abstract class Package implements Built<Package, PackageBuilder>, NamedElement {
     static final Serializer<Package> serializer = _$packageSerializer;
  +
     String get name;
     BuiltSet<Classifier> get classifiers;
   
  
positive.code:   String derivedExpression;
  
    PropertyBuilder._();
    factory PropertyBuilder() = _$PropertyBuilder;
  }
  
  
negative.code:   Classifier bound;
  
    TypeParameterBuilder._();
  
    factory TypeParameterBuilder() = _$TypeParameterBuilder;
  }
  
  abstract class Property
      implements Built<Property, PropertyBuilder>, NamedElement {
    static final Serializer<Property> serializer = _$propertySerializer;
  
    String get name;
    Classifier get type;
    bool get isNullable;
    @nullable
    Object get defaultValue;
    @nullable
    String get derivedExpression;
    bool get isDerived => derivedExpression != null;
  
    Property._();
  