[tdwg-tapir] search with no result

I found an unsolved problem in my pywrapper notes today regarding envelope-less operations. If I request a TAPIR GET service search operation which doesnt match any results, what should be returned?

Without an envelope this would be an empty document without even a root! Should we turn on the envelope in this case? Or return something like <NULL> or <NoMatches> defined by the protocol?

Markus