NIFI-14123: support kafka tombstone with USE_WRAPPER strategy

[babubabu]

Add possibility to leave out the "value" attribute in flowfile wrapper to support publishing kafka tombstones. With this solution, we support a wrapper either completely without the "value" attribute or with "value: null". The JSON Reader and AVRO Set writer support null values out-of-the-box

Summary

NIFI-14123

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  • JDK 21

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[greyp9]

Hi @babubabu; thanks for the contribution! Looks like the "integration-tests" CI failed on this PR for the new test that was added. You can easily run this single test (after a full build) with a command line something like this:

nifi/nifi-extension-bundles/nifi-kafka-bundle % mvn verify -P integration-tests -pl nifi-kafka-3-integration -Dit.test=PublishKafkaWrapperX6IT

[babubabu]

Hi @greyp9 ,
Thanks for your response. Yes I saw it, but couldn't fix it easily yesterday. I'm on it at 2nd Jan ;-)
Happy new year :-)

[babubabu]

Hello @greyp9,
I fixed the test setup, now it should work ;-)
Can you please review it again?

[babubabu]

Fixed checkstyle violations and rebased to current main