API: Don't debug output when exception reaches wsgi layer

Unless of course we ask for it

Change-Id: Iab51e854bca3b21b83133dd44ebc6bdd8641e2fd
API: fix empty responses

WSME json encodes empty strings to return resulting in '""' response
We now override that behaviour to return a true empty response

Change-Id: I1437c5a69723af02ccaa7cda4acef4ffdbae5d4d