PaymentRequest: The currencySystem should be non-nullable.

components/payments/payment_details_validation.cc

Index: components/payments/payment_details_validation.cc
diff --git a/components/payments/payment_details_validation.cc b/components/payments/payment_details_validation.cc
index 81c42cdbb4924298c0e2f32f831986b48a999677..5fce52febfc8f32b98308cd7a6c3eae4601c19d2 100644
--- a/components/payments/payment_details_validation.cc
+++ b/components/payments/payment_details_validation.cc
@@ -44,16 +44,13 @@ bool validateShippingOptionOrPaymentItem(
     return false;
   }
 
-  if (item->amount->currency_system.has_value() &&
-      item->amount->currency_system.value().empty()) {
+  if (item->amount->currency_system.empty()) {
     *error_message = "Currency system can't be empty";
     return false;
   }
 
   if (!payments::PaymentsValidators::isValidCurrencyCodeFormat(
-          item->amount->currency, item->amount->currency_system.has_value()
-                                      ? item->amount->currency_system.value()
-                                      : "",
+          item->amount->currency, item->amount->currency_system,
           error_message)) {
     return false;
   }