The default value of an optional parameter must be constant. Cubit

Question

I have this code and I get the following error: The default value of an optional parameter must be constant. I have searched this problem on the internet, but putting it as constant does not solve the problem, I would like to understand why this happens. This is the code where the error occurs:

part of 'isar_bbdd_repository_cubit.dart';

class IsarBbddRepositoryState extends Equatable{

  final IsarBbddRepositoryImpl isarBbddRepositoryImpl;

  const IsarBbddRepositoryState({
    this.isarBbddRepositoryImpl = IsarBbddRepositoryImpl(IsarBbddDatasourceImpl()) //ERROR
  });

  copyWith({
    IsarBbddRepositoryImpl? isarBbddRepositoryImpl,
  }) => IsarBbddRepositoryState(
    isarBbddRepositoryImpl: isarBbddRepositoryImpl ?? this.isarBbddRepositoryImpl
  );
  
  @override
  List<Object?> get props => [isarBbddRepositoryImpl]; 

}

This is the code for IsarBbddRepositoryImpl:

import 'package:isar/isar.dart';
import 'package:racha_app/domain/datasource/isar_bbdd_datasource.dart';
import 'package:racha_app/domain/repository/isar_bbdd_repository.dart';

class IsarBbddRepositoryImpl extends IsarBbddRepository{

  final IsarBbddDatasource datasource;

  IsarBbddRepositoryImpl(this.datasource);

  @override
  Future<void> delete({required Id isarID, required String uuid}) {
    return datasource.delete(isarID: isarID, uuid: uuid);
  }

This is the IsarBbddDatasourceImpl code (not yet implemented):

import 'package:isar/isar.dart';
import 'package:racha_app/domain/datasource/isar_bbdd_datasource.dart';

class IsarBbddDatasourceImpl extends IsarBbddDatasource{

  @override
  Future<void> delete({required Id isarID, required String uuid}) {
    // TODO: implement delete
    throw UnimplementedError();
  }
  
}

I have tried setting the values as constants, but it does not work.