Added config to control the behavior of check on null values in redis-cache extension

[anadinema]

Implementation to achieve #42184

Please let me know if this is not at all suitable, or if suitable then do let me know if any fixes needed or if I missed something.

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[gsmet]

@anadinema FYI, @cescoffier is on PTO so you'll get feedback when he's back.

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[cescoffier]

LGTM.

Can you rebase your PR?

[anadinema]

@cescoffier done ✅ Hope it's good to merge.

[cescoffier]

I actually want to discuss this with @karesti and @Ladicek when they are back from PTO and handle null the same way in infinispan and redis cache.

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[karesti]

@cescoffier great that is happening! :) IMO this could be the cache extension SPI contract instead of having it specific to Redis since this looks more a generic behaviour of the caching api system rather than something specific to Redis

[cescoffier]

@karesti yes.

Also, I would like to discuss a change the the cache SPI to distinguished a cached null value from a cache miss (as in term of metrics it's totally different)

[anadinema]

@cescoffier let me know, in case the changes are to be made in the cache SPI itself. I can give it a try.

[Ladicek]

I'm not sure if Infinispan can store null values, but the only option in Redis would be to encode it using some sort of a sentinel value, one that is super unlikely to be used by applications. For example, a string "io.quarkus.cache.redis.nullValuePlaceholder". Otherwise, all null values will in fact be cache misses, which is bad.

[karesti]

I'm not sure if Infinispan can store null values, but the only option in Redis would be to encode it using some sort of a sentinel value, one that is super unlikely to be used by applications. For example, a string "io.quarkus.cache.redis.nullValuePlaceholder". Otherwise, all null values will in fact be cache misses, which is bad.

Infinispan can do it, we handle this case with protostream and with java too, to provide null value caching for spring cache