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

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 2.4.0
• Fix Version/s: 2.5.0, 2.4.1
• Component/s: streams
• Assignee: John Roesler
• Reporter: Paul Snively
• Created: 06/Feb/20 19:51
• Updated: 23/Sep/20 08:51
• Resolved: 10/Feb/20 22:15

Description

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] 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.

Issue Links

• duplicates: KAFKA-9248 Foreign key join does not pickup default serdes and dies with NPE
• relates to: KAFKA-10515 NPE: Foreign key join serde may not be initialized with default serde if application is distributed
• links to: GitHub Pull Request #8061