flutter - 使用 dartz 选项> 如何设置为无

Question

我正在尝试使用一种类型Option<Either<T,T>并希望将其设置为 anone()但这会导致错误失败Invalid constant value.dart(invalid_constant)。

如何将选项设置为无或未定义状态。

@freezed
abstract class InvitationsState with _$InvitationsState {
  const factory InvitationsState({
    @required String email,
    @required bool isSubmitting,
    @required bool userAlreadyInvited,
    Option<Either<IRepositoryFailure, Stream<QuerySnapshot>>> snapshotOrFailure,
  }) = _InvitationsState;

  factory InvitationsState.initial() => const InvitationsState(
        email: "",
        isSubmitting: false,
        userAlreadyInvited: false,
        snapshotOrFailure: none(),
      );
}