anchor.diff:  import 'package:crypto/crypto.dart' show sha256;
   import 'package:mongo_dart/mongo_dart.dart';
   import '../models/user.dart';
  +import '../validators/user.dart';
   export '../models/user.dart';
   
   configureServer(Db db) {
  
positive.code:     app.container.singleton(service.inner);
  
      service.beforeCreated
        ..listen(validateEvent(
            new Validator({
              'username*': [isString, isNotEmpty],
              'password*': [isString, isNotEmpty],
              'email*': [isString, isNotEmpty, isEmail],
            }),
            errorMessage:
                'User must have a username, e-mail address and password.'))
        ..listen((e) {
          e.data['password'] = hashPassword(e.data['password']);
        });
  
negative.code: /// Here, we extended the base service class. This allows to only expose
  /// specific methods, and also allows more freedom over things such as validation.
  class UserService extends Service {
    TypedService<User> _inner;
  
    UserService(DbCollection collection) : super() {
      _inner = new TypedService<User>(new MongoService(collection));
    }
  
    @override
  