구매 정보를 저장하는 리포지터리 샘플
 public PaymentController(
     IPaymentsApi paymentsApi,
     CheckoutRepository checkoutRepository,
     PaymentRepository paymentRepository,
     IamportHttpClientOptions clientOptions)
 {
     if (paymentsApi == null)
     {
         throw new ArgumentNullException(nameof(paymentsApi));
     }
     if (checkoutRepository == null)
     {
         throw new ArgumentNullException(nameof(checkoutRepository));
     }
     if (paymentRepository == null)
     {
         throw new ArgumentNullException(nameof(paymentRepository));
     }
     if (clientOptions == null)
     {
         throw new ArgumentNullException(nameof(clientOptions));
     }
     this.paymentsApi = paymentsApi;
     this.checkoutRepository = checkoutRepository;
     this.paymentRepository = paymentRepository;
     iamportId = clientOptions.IamportId;
 }
 public CheckoutController(
     CheckoutRepository checkoutRepository,
     IamportHttpClientOptions clientOptions)
 {
     if (checkoutRepository == null)
     {
         throw new ArgumentNullException(nameof(checkoutRepository));
     }
     if (clientOptions == null)
     {
         throw new ArgumentNullException(nameof(clientOptions));
     }
     this.checkoutRepository = checkoutRepository;
     this.clientOptions = clientOptions;
 }