Rebar doesn't respect mime type setting

[serj-p]

I have an endpoint which returns pdf file. Thus I do something that converts into

registry.add_handler(*args, response_body_schema={200: None}, mimetype='application/pdf').
I want to say that normal reponse code is 200 and marshmallow schema is not applicable. (I used the same technique in order to return just string issue #184 )
later I get

 trace="Traceback (most recent call last):
  File "/opt/opsta/hub-live/py/lib/python2.7/site-packages/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/opt/opsta/hub-live/py/lib/python2.7/site-packages/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/opt/opsta/hub-live/py/lib/python2.7/site-packages/flask_rebar/rebar.py", line 156, in wrapped
    data=data, status_code=status_code, headers=headers, mimetype=mimetype
  File "/opt/opsta/hub-live/py/lib/python2.7/site-packages/flask_rebar/utils/request_utils.py", line 66, in response
    resp = jsonify(data) if data is not None else Response()
  File "/opt/opsta/hub-live/py/lib/python2.7/site-packages/flask/json.py", line 263, in jsonify
    (dumps(data, indent=indent, separators=separators), '\n'),
  File "/opt/opsta/hub-live/py/lib/python2.7/site-packages/flask/json.py", line 123, in dumps
    rv = _json.dumps(obj, **kwargs)
  File "/usr/lib64/python2.7/json/__init__.py", line 251, in dumps
    sort_keys=sort_keys, **kw).encode(obj)
  File "/usr/lib64/python2.7/json/encoder.py", line 209, in encode
    chunks = list(chunks)
  File "/usr/lib64/python2.7/json/encoder.py", line 442, in _iterencode
    o = _default(o)
  File "/opt/opsta/hub-live/py/lib/python2.7/site-packages/hub/core/json.py", line 16, in default
    return super(HubJSONEncoder, self).default(obj)
  File "/opt/opsta/hub-live/py/lib/python2.7/site-packages/flask/json.py", line 80, in default
    return _json.JSONEncoder.default(self, o)
  File "/usr/lib64/python2.7/json/encoder.py", line 184, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: <Response streamed [200 OK]> is not JSON serializable
"

so rebar doesn't care that return content type is not a json, so there's no need to apply json serialization and it doesn't tell swagger that this endpoint returns pdf, but lies about json.