Reactive `multiGet` returns empty string on non-existing key

[dittos]

Reactive multiGet does not distinguish between null and empty string.

// redis: ReactiveStringRedisTemplate instance
redis.opsForValue().set("a", "").block()
val result = redis.opsForValue().multiGet(listOf("a", "nonexisting")).block()!!
println(result) // expects ["", null] but actually ["", ""]

The behavior is inconsistent with Reactive get and blocking multiGet which returns null on non-existing key.

(Tested on spring-data-redis 2.6.2)

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LettuceReactiveStringCommands needs to be changed. (but it would break existing usages)

spring-data-redis/src/main/java/org/springframework/data/redis/connection/lettuce/LettuceReactiveStringCommands.java

Line 73 in 7d34afb

return cmd.mget(keys.toArray(new ByteBuffer[0])).map((value) -> value.getValueOrElse(EMPTY_BYTE_BUFFER))

[mp911de]

See also #2210

[Manasadaram]

I am still observing the issue in version 3.0.1