async Task IDeckService.FavouriteDeckAsync(int id, int userId, bool favourite, CancellationToken cancellationToken) { var deck = await _deckRepository.GetDeckByIdAsync(id, userId, cancellationToken : cancellationToken); if (deck == null) { throw new InvalidDeckException($"Deck { id } does not exist."); } await _deckRepository.FavouriteDeckAsync(id, userId, favourite, cancellationToken : cancellationToken); }