anchor.diff:  }
   
   abstract class PackageBuilder implements Builder<Package, PackageBuilder> {
  +  @nullable
  +  String docComment;
     String name;
     SetBuilder<Classifier> classifiers = new SetBuilder<Classifier>();
   
  
positive.code: abstract class Package implements Built<Package, PackageBuilder>, NamedElement {
    static final Serializer<Package> serializer = _$packageSerializer;
  
    String get name;
    BuiltSet<Classifier> get classifiers;
  
  
negative.code: }
  
  abstract class PropertyBuilder implements Builder<Property, PropertyBuilder> {
    @nullable
    String docComment;
    String name;
    Classifier type;
    bool isNullable = false;
  