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https://issues.apache.org/jira/browse/KAFKA-8671?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16891216#comment-16891216
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Matthias J. Sax commented on KAFKA-8671:
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No reason. Go ahead :)
> NullPointerException occurs if topic associated with GlobalKTable changes
> -------------------------------------------------------------------------
>
> Key: KAFKA-8671
> URL: https://issues.apache.org/jira/browse/KAFKA-8671
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.0.0
> Reporter: Alex Leung
> Priority: Critical
>
> The following NullPointerException occurs when the global/.checkpoint file
> contains a line with a topic previously associated with (but no longer
> configured for) a GlobalKTable:
> {code:java}
> java.lang.NullPointerException
> at
> org.apache.kafka.streams.processor.internals.GlobalStateUpdateTask.update(GlobalStateUpdateTask.java:85)
> at
> org.apache.kafka.streams.processor.internals.GlobalStreamThread$StateConsumer.pollAndUpdate(GlobalStreamThread.java:241)
> at
> org.apache.kafka.streams.processor.internals.GlobalStreamThread.run(GlobalStreamThread.java:290){code}
>
> After line 84
> ([https://github.com/apache/kafka/blob/2.0/streams/src/main/java/org/apache/kafka/streams/processor/internals/GlobalStateUpdateTask.java#L84)]
> `sourceNodeAndDeserializer` is null for the old, but still valid, topic.
> This can be reproduced with the following sequence:
> # create a GlobalKTable associated with topic, 'global-topic1'
> # change the topic associated with the GlobalKTable to 'global-topic2'
> ## at this point, the global/.checkpoint file will contain lines for both
> topics
> # produce messages to previous topic ('global-topic1')
> # the consumer will attempt to consume from global-topic1, but no
> deserializer associated with global-topic1 will be found and the NPE will
> occur
> It looks like the following recent commit has included checkpoint validations
> that may prevent this issue:
> https://github.com/apache/kafka/commit/53b4ce5c00d61be87962f603682873665155cec4#diff-cc98a6c20f2a8483e1849aea6921c34dR425
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