[GitHub] [kafka] jlprat commented on a change in pull request #11241: KAFKA-13032: add NPE checker for KeyValueMapper

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jlprat commented on a change in pull request #11241:
URL: https://github.com/apache/kafka/pull/11241#discussion_r694629688



##########
File path: streams/src/test/java/org/apache/kafka/streams/kstream/internals/KStreamMapTest.java
##########
@@ -68,6 +70,12 @@ public void testMap() {
         }
     }
 
+    @Test
+    public void testKeyValueMapperResultNotNull() {
+        final KStreamMap<String, Integer, String, Integer> supplier = new KStreamMap<>((key, value) -> null);
+        assertThrows(NullPointerException.class, () -> supplier.get().process(new Record<>("K", 0, 0L)));

Review comment:
       Same as previous comment

##########
File path: streams/src/test/java/org/apache/kafka/streams/kstream/internals/KStreamFlatMapTest.java
##########
@@ -86,4 +88,10 @@ public void testFlatMap() {
             assertEquals(expected[i], supplier.theCapturedProcessor().processed().get(i));
         }
     }
+
+    @Test
+    public void testKeyValueMapperResultNotNull() {
+        final KStreamFlatMap<String, Integer, String, Integer> supplier = new KStreamFlatMap<>((key, value) -> null);
+        assertThrows(NullPointerException.class, () -> supplier.get().process(new Record<>("K", 0, 0L)));

Review comment:
       As the whole point of this PR is to provide better messages, I would also check in the test that the exception has the new enhanced message. Something like 
   ```suggestion
           final Record<String, Integer> record = new Record<>("K", 0, 0L);
           assertThrows(NullPointerException.class, () -> supplier.get().process(record), String.format("KeyValueMapper can't return null from mapping the record: %s", record));
   ```




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