From https://github.com/apache/guacamole-client/pull/336#discussion_r241549475:
>
> SLF4J formerly recommended that instance variables be used
> (non-static), but no longer takes either stance:
> https://www.slf4j.org/faq.html#declared_static
>
> If we have to pick something to be the standard going forward, I'd
> say let's stick with the accepted idiom of `private static final`
> loggers, with the exception being where it's actually necessary to
> not be `static` (dependency injection).
>
