Value parameters in ReactiveKafkaProducerTemplate should be nullable

[aelfric]

In what version(s) of Spring for Apache Kafka are you seeing this issue?

For example:

3.1.1 - but seems like this is true in the latest versions too

Describe the bug

Similar to #1825 the @NonNullApi applied to the
package org.springframework.kafka.core.reactive means that static analysis tools think it is not possible to pass null into org.springframework.kafka.core.reactive.ReactiveKafkaProducerTemplate#send(java.lang.String, K, V), but null is allowed and required if we want to publish null tombstone messages.

To Reproduce

Create a ReactiveKafkaProducerTemplate instance and call send on it with a value of null, run SonarLint on that class.

Expected behavior

The value parameter in this method and the other related methods should be annotated as nullable.

[artembilan]

Good catch!
Feel free to contribute the fix: https://github.com/spring-projects/spring-kafka/blob/main/CONTRIBUTING.adoc

[jukekxm]

@artembilan @aelfric Hello. if you are not working on this, can I work on it?

[aelfric]

I was going to work on it, but I've had trouble building the project under my company's firewall and haven't had a chance to get the issues resolved. If you want to make the change, go ahead.

[jukekxm]

@aelfric Thank you!
I will create PR for this issue.

[jukekxm]

#3651
I created PR.
I would appreciate it if you could review!