This is not really a bug per se, but a backward incompatible change that affects current Picard installations and possible other software.
On the current live server, if you query the webservice for a release with the inc=collections parameter and you don't have this release in any of your collections, the <collection-list> node will be omitted:
If you do the same on the current beta, an empty "<collection-list count="0"/>" will be part of the result:
I would advise in fixing this, even though this is arguably a bug in Picard (I will make sure it gets fixed there, too). But if this code goes live it will affect a large amount of users, and rolling out a new Picard release is, despite us releasing Picard not very often, a slow process nevertheless.