public class Payment : ValueObject
    {
        public DateTime PaymentDate { get; private set; }
        public PaymentType PaymentType { get; private set; }

        public static Payment CreateMoney(DateTime paymentDate)
        {
            return new Payment
                   {
                       PaymentType = PaymentType.MoneyPayment,
                       PaymentDate = paymentDate
                   };
        }

        public static Payment CreateFree(DateTime paymentDate)
        {
            return new Payment
                   {
                       PaymentType = PaymentType.FreePayment,
                       PaymentDate = paymentDate
                   };
        }
    }