use correct default value - a sub
Always deserialize: two bugs fixed:

While writing a serializer, I noticed the following bugs:

* We check for a reference before serialize content. This is wrong
  for two reasons: some serializers serialize non-refs (CBOR), and
  some when a serializer is configured, we should try to serialize
  anyway.

* We only serialized if we matched the content-type. This is wrong.
  The content type is for output, not input. It is, in fact, also
  used by the Mutable serializer, but that's beside the point.

This commit contains the following changes:

* Always try to serialize the content in the response (even if it's
not a reference).

* Always try to serialize the content in the response (even if the
content type says something different).
for cleanups sake
reflect change
Merge branch 'fix/serializers'