[GitHub] [flink] AHeise commented on a change in pull request #16142: [FLINK-22748][connector-kafka] Allow dynamic target topic selection in SQL Kafka sinks

[GitBox <gi...@apache.org>]

AHeise commented on a change in pull request #16142:
URL: https://github.com/apache/flink/pull/16142#discussion_r658231896



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File path: flink-connectors/flink-connector-kafka/src/main/java/org/apache/flink/streaming/connectors/kafka/FlinkKafkaProducer.java
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@@ -216,7 +216,7 @@
     protected final Properties producerConfig;
 
     /** The name of the default topic this producer is writing data to. */
-    protected final String defaultTopicId;
+    @Nullable protected String defaultTopicId;

Review comment:
       I don't understand why we need to make default topic nullable. We could just set "unspecified" on table API if there is no other value. Potentially add some special character that kafka doesn't support to make sure writing fails.
   As is, we change quite a bit of API and semantics and introduce new bugs (there is no guard against `defaultTopicId = null` and `getTargetTopic = null`).
   Another idea would be to explicitly support default topic option with said default value.  




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