public async Task <bool> DenyRental(Rental rental)
        {
            if (rental == null)
            {
                return(false);
            }

            database.AdminRepository.Remove <Rental>(rental);

            await notificationSystem.PushNotification(rental.OwnerId, StaticExpressions.RentalDenied(rental.Name), NotificationType.Rental);

            return(await database.Complete());
        }