invoice: fix NPE in ItemsInterval.createNewItem

Handle the case where there is nothing to pro-rate, because the original
item has already been fully repaired or adjusted.

This fixes #286.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>

invoice/src/main/java/org/killbill/billing/invoice/tree/Item.java

@@ -1,7 +1,9 @@
 /*
  * Copyright 2010-2014 Ning, Inc.
+ * Copyright 2014-2015 Groupon, Inc
+ * Copyright 2014-2015 The Billing Project, LLC
  *
- * Ning licenses this file to you under the Apache License, version 2.0
+ * The Billing Project licenses this file to you under the Apache License, version 2.0
  * (the "License"); you may not use this file except in compliance with the
  * License.  You may obtain a copy of the License at:
  *
@@ -184,7 +186,9 @@ public boolean isSameKind(final Item other) {
 
         final InvoiceItem otherItem = other.toInvoiceItem();
 
-        return !id.equals(otherItem.getId()) &&
+        // See https://github.com/killbill/killbill/issues/286
+        return otherItem != null &&
+               !id.equals(otherItem.getId()) &&
                // Finally, for the tricky part... In case of complete repairs, the new invoiceItem will always meet all of the
                // following conditions: same type, subscription, start date. Depending on the catalog configuration, the end
                // date check could also match (e.g. repair from annual to monthly). For that scenario, we need to default

invoice/src/main/java/org/killbill/billing/invoice/tree/ItemsInterval.java

@@ -1,7 +1,9 @@
 /*
  * Copyright 2010-2014 Ning, Inc.
+ * Copyright 2014-2015 Groupon, Inc
+ * Copyright 2014-2015 The Billing Project, LLC
  *
- * Ning licenses this file to you under the Apache License, version 2.0
+ * The Billing Project licenses this file to you under the Apache License, version 2.0
  * (the "License"); you may not use this file except in compliance with the
  * License.  You may obtain a copy of the License at:
  *
@@ -27,6 +29,7 @@
 import java.util.UUID;
 
 import org.joda.time.LocalDate;
+import org.killbill.billing.invoice.api.InvoiceItem;
 import org.killbill.billing.invoice.tree.Item.ItemAction;
 
 import com.google.common.base.Preconditions;
@@ -227,15 +230,20 @@ public int size() {
      * @param mergeMode mode to consider.
      * @return
      */
-    private Item createNewItem(LocalDate startDate, LocalDate endDate, final boolean mergeMode) {
+    private Item createNewItem(final LocalDate startDate, final LocalDate endDate, final boolean mergeMode) {
 
         final Item item = getResultingItem(mergeMode);
         if (item == null) {
             return null;
         }
 
-        final Item result = new Item(item.toProratedInvoiceItem(startDate, endDate), targetInvoiceId, item.getAction());
-        if (item.getAction() == ItemAction.CANCEL && result != null) {
+        final InvoiceItem proratedInvoiceItem = item.toProratedInvoiceItem(startDate, endDate);
+        if (proratedInvoiceItem == null) {
+            return null;
+        }
+
+        final Item result = new Item(proratedInvoiceItem, targetInvoiceId, item.getAction());
+        if (item.getAction() == ItemAction.CANCEL) {
             item.incrementCurrentRepairedAmount(result.getAmount());
         }
         return result;

invoice/src/test/java/org/killbill/billing/invoice/tree/TestSubscriptionItemTree.java

@@ -855,6 +855,32 @@ public void verifyJson() {
         }
     }
 
+    @Test(groups = "fast", description = "https://github.com/killbill/killbill/issues/286")
+    public void testMaxedOutProRation() {
+        final LocalDate startDate = new LocalDate(2014, 1, 1);
+        final LocalDate cancelDate = new LocalDate(2014, 1, 25);
+        final LocalDate endDate = new LocalDate(2014, 2, 1);
+
+        final BigDecimal monthlyRate1 = new BigDecimal("12.00");
+        final BigDecimal monthlyAmount1 = monthlyRate1;
+
+        final SubscriptionItemTree tree = new SubscriptionItemTree(subscriptionId, invoiceId);
+
+        final InvoiceItem existing1 = new RecurringInvoiceItem(invoiceId, accountId, bundleId, subscriptionId, planName, phaseName, startDate, endDate, monthlyAmount1, monthlyRate1, currency);
+        tree.addItem(existing1);
+        // Fully item adjust the recurring item
+        final InvoiceItem existingItemAdj1 = new ItemAdjInvoiceItem(existing1, startDate, monthlyRate1.negate(), currency);
+        tree.addItem(existingItemAdj1);
+        tree.flatten(true);
+
+        final InvoiceItem proposed1 = new RecurringInvoiceItem(invoiceId, accountId, bundleId, subscriptionId, planName, phaseName, startDate, cancelDate, monthlyAmount1, monthlyRate1, currency);
+        tree.mergeProposedItem(proposed1);
+        tree.buildForMerge();
+
+        final List<InvoiceItem> expectedResult = Lists.newLinkedList();
+        verifyResult(tree.getView(), expectedResult);
+    }
+
     private void verifyResult(final List<InvoiceItem> result, final List<InvoiceItem> expectedResult) {
         assertEquals(result.size(), expectedResult.size());
         for (int i = 0; i < expectedResult.size(); i++) {