Today the question came up at work if it is allowed to have extra commas in debian/control dependency fields as in

Depends: ${misc:Depends}, ${shlib:Depends}

The substitution misc:Depends may well be empty. So is this allowed?

It actually is as Tollef Fog Heen quickly replied on IRC (thanks). It is also covered by a test case in the dpkg source tree, so it is unlikely to go away.

There seems to be no documentation about it though (neither policy nor manual pages cover this). Maybe I will send a patch.