Fixed storing and loading nulls and booleans in Redis

See #1311 

- [ ] Fix `LuaScriptBuilder` to use `HEXISTS` in case of `null` values instead of comparison.
- [x] Fix `LuaScriptBuilder` to cast booleans to 0 or 1 before using these in conditions.
yeah, but we can adjust that for redis, it uses quite some effort to add attributes that can be checked by empty() or isset() without problem later. Redis is used mainly because it is really fast so we should avoid such adjustments as they do not bring any value.