Flutter: NoSuchMethodError: Closure call with mismatched arguments: function 'Global.models.<anonymous closure>'

I am building my own flutter app with the help of the Flutter Firebase course from fireship.io. The courses repository is here.

However, since abandoning multiple streams - from my own tries before starting the course - in favor of classes with anonymous types, I receive the following error message and can't get my head around why.

Goal: I want a Stream with all documents from any firestore collection, in this case 'hochschulen'. The Collection exists and is filled with data. All fields are Strings.

Expected: No error message

Actual Result:

flutter: The following assertion was thrown:
flutter: An exception was throw by _MapStream<QuerySnapshot, List<University>> listened by
flutter: StreamProvider<List<University>>, but no `catchError` was provided.
flutter:
flutter: Exception:
flutter: NoSuchMethodError: Closure call with mismatched arguments: function 'Global.models.<anonymous
flutter: closure>'
flutter: Receiver: Closure: (dynamic, String) => University
flutter: Tried calling: Global.models.<anonymous closure>(data: _LinkedHashMap len:10)
flutter: Found: Global.models.<anonymous closure>(dynamic, String) => University
flutter:
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════

I have tried:

• defining all expected types of all parameters
• I have looked at this and this and some more similar questions, but struggle to adapt to my code, because I can't find missing parameters.
• I do believe I understand that this issue probably occures because some type and/or parameter of something is mixed up or missing.

This is the widget where I want to load some data:

class LegalScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamProvider<List<University>>.value(
      value: Global.universityRef.streamData(),
      child: LegalScreenContent(),
    );
  }
}

This is my global class:

class Global {
  static final FirebaseAnalytics analytics = FirebaseAnalytics();
  static final Map models = {
    // Dish: (data, id) => Dish.fromMap(data, id),
    // Event: (data, id) => Event.fromMap(data, id),
    // News: (data, id) => News.fromMap(data, id),
    // Subject: (data, id) => Subject.fromMap(data, id),
    University: ({Map data}) => University.fromMap(data: data),
    // UserModel: (data, id) => UserModel.fromMap(data, id),
  };
  static final UserData<UserModel> userModelRef =
      UserData<UserModel>(collection: 'users');
  static final Collection<University> universityRef =
      Collection<University>(path: 'hochschulen');
}

Here is the model for University:

class University {
  String city;
  String domain;
  String mail;
  String name;
  String shortName;
  String street;
  String phone;
  String website;
  String zip;
  University(
      {this.city,
      this.domain,
      this.mail,
      this.name,
      this.shortName,
      this.street,
      this.phone,
      this.website,
      this.zip});
  University.fromMap({Map data}) {
    city = data['city'] ?? '';
    domain = data['domain'] ?? '';
    mail = data['mail'] ?? '';
    name = data['name'] ?? '';
    shortName = data['short_name'] ?? '';
    street = data['street'] ?? '';
    phone = data['tel'] ?? '';
    website = data['website'] ?? '';
    zip = data['zip'] ?? '';
  }
}

Here is my Collection class:

class Collection<T> {
  final FirebaseFirestore _db = FirebaseFirestore.instance;
  final String path;
  CollectionReference ref;
  Collection({this.path}) {
    ref = _db.collection(path);
  }
  Future<List<T>> getData() async {
    var snapshots = await ref.get();
    return snapshots.docs
        .map((doc) => Global.models[T](doc.data, doc.id) as T)
        .toList();
  }
  Stream<List<T>> streamData() {
    return ref.snapshots().map((snapshot) => snapshot.docs
        .map((doc) => Global.models[T](data: doc.data()) as T)
        .toList());
  }
}