iTunes Search API UPC Lookup

Hi,

It seems that some requests from the iTunes Search APIhave stopped working. Try looking at the Lookup Examples:

Look up an album or video by its UPC:
https://itunes.apple.com/lookup?upc=720642462928

This produces a newNullResponse.

Has Apple deprecated them? My application relies on them and I'd love to know if it's just a temporary bug or a permanent change.
Thank you for any help you can offer!