Thanks Florin for the writeup, One quick thing I'd like to bring up is that in KIP-149 (https://cwiki.apache.org/confluence/display/KAFKA/KIP-149%3A+Enabling+key+access+in+ValueTransformer%2C+ValueMapper%2C+and+ValueJoiner) we introduced ValueJoinerWithKey which is aimed to enhance ValueJoiner. It would have a benefit for this KIP such that implementers can distinguish "null-key" v.s. "not-null-key but null-value" scenarios.
Hence I'd suggest we also include the semantic changes with ValueJoinerWithKey, which can help distinguish these two scenarios, and also document that if users apply ValueJoiner only, they may not have this benefit, and hence we suggest users to use the former. Guozhang On Mon, Jul 31, 2023 at 12:11 PM Florin Akermann <florin.akerm...@gmail.com> wrote: > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-962%3A+Relax+non-null+key+requirement+in+Kafka+Streams
