Error with 204 response having a content-type.

As per RFC 2616:
##### [10.2.5](http://tools.ietf.org/html/rfc2616#section-10.2.5) 204 No Content:
> The response MAY include ... metainformation in the form of entity-headers

##### [7.1](http://tools.ietf.org/html/rfc2616#section-7.1) Entity Header Fields
Content-Type is an entity-header.

A 204 response can have a content type.