[BUG] Tag cache with empty values

[regorxxx]

Describe the bug
Tags not found on files may return a '?' or '' when having brackets.

Expected behavior
'' values are probably fine, since there must be a way to show the file has no tag, although array could be empty too.
? values should probably be filtered though. They are filtered now on the genre/style retrieval, but should be done globally.

Additional context
Add any other context about the problem here.

[regorxxx]

Tag cache is now deprecated and there is no need to do anything more with this.