when iterating over item keys, do not return duplicates
when iterating over item keys, do not return duplicates

... for keys that exist both as Item and Album fields

beetbox/beets,ibmibmibm/beets,beetbox/beets,beetbox/beets,ibmibmibm/beets,ibmibmibm/beets,ibmibmibm/beets,beetbox/beets