When the value of fqcn (fully qualified class name) for
LocationAwareLogger.log() is wrong, logging frameworks like logback log "?" as
location.

Change the documentation of the method to say "the implementation should print
'fqcn not found:' plus the wrong value of fqcn when the value can't be found in
the stack trace".

This will make the error more obvious and easier to fix.

Can you make this change in logback or should I file another issue?