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https://issues.apache.org/jira/browse/KAFKA-20823?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lucy Liu reassigned KAFKA-20823:
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Assignee: Lucy Liu (was: Matthias J. Sax)
> Relax null-value restriction in Kafka Streams joins
> ---------------------------------------------------
>
> Key: KAFKA-20823
> URL: https://issues.apache.org/jira/browse/KAFKA-20823
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Matthias J. Sax
> Assignee: Lucy Liu
> Priority: Minor
> Labels: needs-kip
>
> Historically, Kafka Streams DSL treats `null` keys or values as malformed
> data in certain cases, and this is still the right thing to do for many
> operators.
> With KIP-962
> ([https://cwiki.apache.org/confluence/spaces/KAFKA/pages/263426175/KIP-962+Relax+non-null+key+requirement+in+Kafka+Streams])
> we lifted some constraints for case in which it does make sense for
> null-keys.
> I believe, we could lift even more restrictions for null-values in KStreams
> and leftJoins (at least left-stream-table joins – not sure about left/outer
> stream-stream join – we want to avoid ambiguity of `null` with could also
> mean "record does not exist" what is semantically different to "record exists
> but has null-value").
> If the left (ie, KStream record) value is null, we could still produce a
> left-join result (it's an open question if we would call the KeyValueMapper
> for stream-globalTable case or not for this case – note, that for
> stream-globalTable join, we already allow KeyValueMapper to also return null,
> and produce a leftJoin result for this case – this is the exact same line of
> thinking).
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