Flutter Freeze and json_serializable to Json using Bloc

Question

I have this BoardState I'm using the Bloc Statement management.

part of 'board_cubit.dart';

@freezed
class BoardState with _$BoardState {
  const BoardState._();

  const factory BoardState.loading() = _Initial;
  const factory BoardState.loaded(List<Board> boards) = _Loaded;
  const factory BoardState.error(String message) = _Error;
  const factory BoardState.selected(String boardId) = _Selected;

  factory BoardState.fromJson(Map<String, dynamic> json) =>
      _$BoardStateFromJson(json);

  Map<String, dynamic> toJson() => _$BoardStateToJson(this);
}

I'm getting this error.

How can I get toJson to Work?