Empty AlbumArtist & displayFormat

[simoncn]

You can do this by creating a new tag whose value is populated from AlbumArtist if present or with the literal value 'VV AA' if there is no AlbumArtist value.

itemTags: add AlbumArtistDisplay
tagValue: AlbumArtistDisplay.default={AlbumArtist, 'VV AA'}
tagFormat: Album.displayFormat={$AlbumArtistDisplay$Album$OwnedLabel^^^ • }