killbill-memoizeit

diff --git a/invoice/src/main/java/org/killbill/billing/invoice/api/user/DefaultInvoiceUserApi.java b/invoice/src/main/java/org/killbill/billing/invoice/api/user/DefaultInvoiceUserApi.java
index 4079b53..7e56ce5 100644
--- a/invoice/src/main/java/org/killbill/billing/invoice/api/user/DefaultInvoiceUserApi.java
+++ b/invoice/src/main/java/org/killbill/billing/invoice/api/user/DefaultInvoiceUserApi.java
@@ -292,6 +292,9 @@ public class DefaultInvoiceUserApi implements InvoiceUserApi {
                     } else {
                         if (existingInvoicesForExternalCharges.get(invoiceIdForExternalCharge) == null) {
                             final Invoice existingInvoiceForExternalCharge = getInvoice(invoiceIdForExternalCharge, context);
+                            if (InvoiceStatus.COMMITTED.equals(existingInvoiceForExternalCharge.getStatus())) {
+                                throw new InvoiceApiException(ErrorCode.INVOICE_ALREADY_COMMITTED, existingInvoiceForExternalCharge.getId());
+                            }
                             existingInvoicesForExternalCharges.put(invoiceIdForExternalCharge, existingInvoiceForExternalCharge);
                         }
                         invoiceForExternalCharge = existingInvoicesForExternalCharges.get(invoiceIdForExternalCharge);

diff --git a/invoice/src/test/java/org/killbill/billing/invoice/api/user/TestDefaultInvoiceUserApi.java b/invoice/src/test/java/org/killbill/billing/invoice/api/user/TestDefaultInvoiceUserApi.java
index aa1ae0b..9dc97b3 100644
--- a/invoice/src/test/java/org/killbill/billing/invoice/api/user/TestDefaultInvoiceUserApi.java
+++ b/invoice/src/test/java/org/killbill/billing/invoice/api/user/TestDefaultInvoiceUserApi.java
@@ -27,6 +27,7 @@ import javax.annotation.Nullable;
 import org.killbill.billing.ErrorCode;
 import org.killbill.billing.ObjectType;
 import org.killbill.billing.account.api.Account;
+import org.killbill.billing.api.TestApiListener.NextEvent;
 import org.killbill.billing.callcontext.DefaultCallContext;
 import org.killbill.billing.catalog.api.Currency;
 import org.killbill.billing.invoice.InvoiceTestSuiteWithEmbeddedDB;
@@ -35,6 +36,7 @@ import org.killbill.billing.invoice.api.InvoiceApiException;
 import org.killbill.billing.invoice.api.InvoiceItem;
 import org.killbill.billing.invoice.api.InvoiceItemType;
 import org.killbill.billing.invoice.api.InvoiceStatus;
+import org.killbill.billing.invoice.api.InvoiceUserApi;
 import org.killbill.billing.invoice.model.ExternalChargeInvoiceItem;
 import org.killbill.billing.util.api.TagApiException;
 import org.killbill.billing.util.callcontext.CallContext;
@@ -373,5 +375,20 @@ public class TestDefaultInvoiceUserApi extends InvoiceTestSuiteWithEmbeddedDB {
         creditInvoice = invoiceUserApi.getInvoice(invoiceId, callContext);
         Assert.assertEquals(creditInvoice.getStatus(), InvoiceStatus.COMMITTED);
 
+        try {
+            final InvoiceItem externalCharge = new ExternalChargeInvoiceItem(invoiceId, accountId, null, "Initial external charge", clock.getUTCToday(), new BigDecimal("12.33"), accountCurrency);
+            invoiceUserApi.insertExternalCharges(accountId, clock.getUTCToday(), ImmutableList.of(externalCharge), true, callContext);
+            Assert.fail("Should fail to add external charge on already committed invoice");
+        } catch (final InvoiceApiException e) {
+            Assert.assertEquals(e.getCode(), ErrorCode.INVOICE_ALREADY_COMMITTED.getCode());
+        }
+
+        try {
+            invoiceUserApi.insertCreditForInvoice(accountId, invoiceId, creditAmount,
+                                                  clock.getUTCToday(), accountCurrency, null, callContext);
+            Assert.fail("Should fail to add credit on already committed invoice");
+        } catch (final InvoiceApiException e) {
+            Assert.assertEquals(e.getCode(), ErrorCode.INVOICE_ALREADY_COMMITTED.getCode());
+        }
     }
 }