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https://issues.apache.org/jira/browse/KAFKA-9517?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17033985#comment-17033985
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John Roesler commented on KAFKA-9517:
-------------------------------------
Quick update, I've merged this fix to trunk, 2.5, and 2.4. I'll go ahead and
mark this ticket resolved so that it doesn't prevent the creation of 2.4.1 or
2.5.0 release candidates.
I'd still very much appreciate it if you can test it to make sure it resolves
the issue for your use case.
> KTable Joins Without Materialized Argument Yield Results That Further Joins
> NPE On
> ----------------------------------------------------------------------------------
>
> Key: KAFKA-9517
> URL: https://issues.apache.org/jira/browse/KAFKA-9517
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.4.0
> Reporter: Paul Snively
> Assignee: John Roesler
> Priority: Blocker
> Fix For: 2.5.0, 2.4.1
>
> Attachments: test.tar.xz
>
>
> The `KTable` API implemented [[here||#L842-L844]]
> [https://github.com/apache/kafka/blob/2.4.0/streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableImpl.java#L842-L844]
> []|#L842-L844]] calls `doJoinOnForeignKey` with an argument of
> `Materialized.with(null, null)`, as apparently do several other APIs. As the
> comment spanning [these lines|#L1098-L1099]] makes clear, the result is a
> `KTable` whose `valueSerde` (as a `KTableImpl`) is `null`. Therefore,
> attempts to `join` etc. on the resulting `KTable` fail with a
> `NullPointerException`.
> While there is an obvious workaround—explicitly construct the required
> `Materialized` and use the APIs that take it as an argument—I have to admit I
> find the existence of public APIs with this sort of bug, particularly when
> the bug is literally documented as a comment in the source code, astonishing
> to the point of incredulity. It calls the quality and trustworthiness of
> Kafka Streams into serious question, and if a resolution is not forthcoming
> within a week, we will be left with no other option but to consider technical
> alternatives.
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