Prior to this commit, requests with an empty body and no Content-Type
header set would fail with a HttpMediaTypeNotSupportedException when
mapped to a Controller method argument annotated with
@RequestBody(required=false).
In those cases, the server implementation considers with an
"application/octet-stream" content type and polls messageconverters for
conversion. If no messageconverter is able to process this request, a
HttpMediaTypeNotSupportedException is thrown.
This change makes sure that such exceptions are not thrown if the
incoming request has:
* no body
* no content-type header
In this case, a null value is returned.
Issue: SPR-13147
e81a430e61