wp_cache_flush_group fails on 2.5.2 about redis-cache

[tillkruss]

@yatsukhnenko: Can you take a look at this. It's probably due to our new lua closures and we didn't test Sentinel enough.

[yatsukhnenko]

@Trisky can you provide configuration which you use so I could replicate issue locally?

[Trisky]

I'm using predis + sentinel. My config looks like this:

WP_REDIS_SENTINEL: website-master
WP_REDIS_DISABLE_DROPIN_AUTOUPDATE: true
WP_REDIS_CLIENT: predis
WP_REDIS_METRICS_MAX_TIME: 10800
WP_REDIS_SERVERS: ['tcp://xxx1.local:26379','tcp://xxx2.local:26379','tcp://xxx3.local:26379']

Plugins and themes installed are kinda irrelevant since it happens with --skip-plugins --skip-themes in the CLI :)

[yatsukhnenko]

OK, the fix in #520 works but there is another problem with sentinel replication connection

PHP Deprecated:  version_compare(): Passing null to parameter #1 ($version1) of type string is deprecated in /var/www/html/wp-content/object-cache.php

@tillkruss should I create another issue for it or just add another commit to my PR?

[tillkruss]

@yatsukhnenko Yes please 👍