killbill-aplcache

diff --git a/payment/src/main/java/org/killbill/billing/payment/api/DefaultPaymentApi.java b/payment/src/main/java/org/killbill/billing/payment/api/DefaultPaymentApi.java
index 656f830..3da498d 100644
--- a/payment/src/main/java/org/killbill/billing/payment/api/DefaultPaymentApi.java
+++ b/payment/src/main/java/org/killbill/billing/payment/api/DefaultPaymentApi.java
@@ -166,7 +166,7 @@ public class DefaultPaymentApi extends DefaultApiBase implements PaymentApi {
     }
 
     @Override
-    public Payment createPurchaseWithPaymentControl(final Account account, @Nullable final UUID paymentMethodId, @Nullable final UUID paymentId, final BigDecimal amount, final Currency currency, final String paymentExternalKey, final String paymentTransactionExternalKey,
+    public Payment createPurchaseWithPaymentControl(final Account account, @Nullable final UUID paymentMethodId, @Nullable final UUID paymentId, final BigDecimal amount, final Currency currency, @Nullable  final String paymentExternalKey, final String paymentTransactionExternalKey,
                                                     final Iterable<PluginProperty> properties, final PaymentOptions paymentOptions, final CallContext callContext) throws PaymentApiException {
         final List<String> paymentControlPluginNames = toPaymentControlPluginNames(paymentOptions);
         if (paymentControlPluginNames.isEmpty()) {
@@ -179,7 +179,6 @@ public class DefaultPaymentApi extends DefaultApiBase implements PaymentApi {
             checkPositiveAmount(amount);
             checkNotNullParameter(currency, "currency");
         }
-        checkNotNullParameter(paymentExternalKey, "paymentExternalKey");
         checkNotNullParameter(paymentTransactionExternalKey, "paymentTransactionExternalKey");
         checkNotNullParameter(properties, "plugin properties");