Type Error

main.dart

typedef ModelConstructor<T1 extends Model<T1>> = T1 Function({
ModelDefinition<T1>? dataType,
DocumentReference<Map<String, dynamic>?>? docRef,
Data? parent,
});

typedef RepositoryConstructor<T1 extends Model<T1>> = Repository<T1> Function();

final Map<Type, ModelConstructor<Model<dynamic>>>
_modelConstructorsByModelType = {};

register<U1 extends Repository<U2>, U2 extends Model<U2>>(
    RepositoryConstructor<U2> repoConstructor,
    ModelConstructor<U2> modelConstructor,
    ) {
  if (_modelConstructorsByModelType.containsKey(U2)) {
    throw Exception('Model type already registered.');
  }

  _modelConstructorsByModelType[U2] = modelConstructor;
  
  //_modelConstructorsByModelType[U2] = modelConstructor as ModelConstructor<Model<dynamic>>; // This does not work either (it compiles, but throws a runtime error)
}

class ModelDefinition<T1 extends Model<T1>> {}

class DocumentReference<T1> {}

class Data {}

abstract class Model<T1 extends Model<T1>> {}

abstract class Repository<T1 extends Model<T1>> {}

main() {}