private Task <Option <Waiter, Error> > CheckIfWaiterExists(Guid waiterId) =>
_waiterRepository
.Get(waiterId)
.WithException(Error.NotFound($"No waiter with an id of {waiterId} was found."));
private Task <Option <Waiter, Error> > WaiterShouldExist(Guid waiterId) =>
_waiterRepository
.Get(waiterId)
.WithException(Error.NotFound($"No waiter with id {waiterId} was found."));
private async Task <Option <Unit, Error> > WaiterShouldntExist(Guid waiterId) =>
(await _waiterRepository.Get(waiterId))
.SomeWhen(w => !w.HasValue, Error.Conflict($"Waiter {waiterId} already exists."))
.Map(_ => Unit.Value);