The Picard default name files script includes the following portion "$if($ne(%albumartist%,),%album%/)". This should be refined adding a trailing comma to make it consistent with the scripting documentation (http://picard.musicbrainz.org/docs/scripting/) and with the rest of the script (all other $if functions include two commas). Here is the suggested revision: "$if($ne(%albumartist%,),%album%/,)".