We now emit false when SET XX/SET NX complete without setting the value because the condition was evaluated to not set the value. Previously, we did not emit a value as Redis responds null (nil). This behavior becomes visible through ReactiveValueOperations.set[ifPresent|ifAbsent](…) methods.
This is a breaking change in the sense that changes the character of ReactiveValueOperations.set[ifPresent|ifAbsent](…) from an optionally emitted element to always emit. Reactive sequences that currently resume operation with .switchIfEmpty(…) will no longer utilize the fallback publisher.
Original pull request: #317.
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