Paul Snively created KAFKA-9517:
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Summary: 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
The `KTable` API implemented
[here|[https://github.com/apache/kafka/blob/2.4.0/streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableImpl.java#L842-L844]]
calls `doJoinOnForeignKey` with an argument of `Materialized.with(null,
null)`, as apparently do several other APIs. As the comment spanning [these
lines|[https://github.com/apache/kafka/blob/2.4.0/streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableImpl.java#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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