public void DeleteEmployee(string userId)
        {
            var employee = GetEmployee(userId);

            if (employee.Id != null && DriverRepository.Remove(employee.Id) == false)
            {
                if (SupervisorRepository.Remove(employee.Id) == false)
                {
                    DispatcherRepository.Remove(employee.Id);
                }
            }
            PersistenceContext.SaveChanges();
        }