According to https://meta.wikimedia.org/wiki/User-Agent_policy and the associated mailing list threads, user agent headers are now required (and have been for some time) but on the request log side, we see a lot of requests with the user agent "-" - IOW, an empty field. Is the blocking of requests absent a user agent simply happening at a 'higher' stage (in mediawiki itself?) and so not registering with the varnishes, or is sending an /empty/ header simply A-OK?