[jira] [Commented] (KAFKA-9517) KTable Joins Without Materialized Argument Yield Results That Further Joins NPE On

["John Roesler (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-9517?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17031893#comment-17031893 ] 

John Roesler commented on KAFKA-9517:
-------------------------------------

Hey [~psnively],

Thanks for the report. I think this is the same as KAFKA-9500 . 

I already have a PR to fix it, although I need to address some comments.

If you like, you could take a look at https://github.com/apache/kafka/pull/8015 to see if it fixes the issue for you.

> 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
>            Priority: Critical
>
> 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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