Basically what I'm doing is this (for example):

1) Start with mp3s that have the Composer field populated (often incorrectly), and run them through Picard.
2) Picard matches them to tracks that don't have composer information.
3) I want a tagging script that says 'if there's no composer information, delete the tag (or make in blank)'. $if($eq(%composer%,),$set(composer,)); does not work, since it just ignores the existing tag. Using a fake value (like a space) is kind of weak.