kafka-streams: capture the ambiguous null tombstone compile error

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01RjfyTgmERTWLqzafu34Cth

kafka-streams/README.md

@@ -39,5 +39,6 @@ Every file in `output/` is written by a test that also asserts it.
 | `04-blocklist-table-join.txt` | Join before blocking, after blocking, and after a tombstone |
 | `05-topology-description.txt` | `Topology.describe()` of the whole graph |
 | `06-spring-context.txt` | The Spring factory bean is wired and not running |
+| `07-ambiguous-null-tombstone.txt` | The real `javac` error for `pipeInput("c5", null)`; source in `src/broken/`, regenerated by `scripts/compile-broken.sh` |
 
 The article carries the explanations; there is deliberately no `docs/` folder.

kafka-streams/output/07-ambiguous-null-tombstone.txt

@@ -0,0 +1,8 @@
+src/broken/AmbiguousNullTombstone.java:9: error: reference to pipeInput is ambiguous
+        blocked.pipeInput("c5", null);
+               ^
+  both method pipeInput(K,V) in TestInputTopic and method pipeInput(V,Instant) in TestInputTopic match
+  where K,V are type-variables:
+    K extends Object declared in class TestInputTopic
+    V extends Object declared in class TestInputTopic
+1 error

kafka-streams/scripts/compile-broken.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+# Captures the real javac error for the null-tombstone mistake into output/07-ambiguous-null-tombstone.txt
+set -uo pipefail
+cd "$(dirname "$0")/.."
+mvn -B -q dependency:build-classpath -Dmdep.outputFile=target/cp.txt >/dev/null
+mkdir -p target/broken
+javac -d target/broken -cp "$(cat target/cp.txt)" src/broken/AmbiguousNullTombstone.java 2>&1 \
+  | grep -v '^Picked up' > output/07-ambiguous-null-tombstone.txt
+cat output/07-ambiguous-null-tombstone.txt

kafka-streams/scripts/run-all.sh

@@ -4,4 +4,5 @@ set -euo pipefail
 cd "$(dirname "$0")/.."
 rm -f output/*.txt
 mvn -B -q test
+scripts/compile-broken.sh >/dev/null || true
 ls output

kafka-streams/src/broken/AmbiguousNullTombstone.java

@@ -0,0 +1,11 @@
+import org.apache.kafka.streams.TestInputTopic;
+
+/**
+ * Deliberately does not compile; it lives outside src/main and src/test so the build ignores it.
+ * scripts/compile-broken.sh runs javac on it and captures the compiler's own message.
+ */
+public class AmbiguousNullTombstone {
+    static void tombstone(TestInputTopic<String, String> blocked) {
+        blocked.pipeInput("c5", null);
+    }
+}