Empty/wrong response if Content-Type is missing

[MV88]

If the Content-Type is missing in mimetypeWhitelist it returns a 200 Ok with an empty body
it would be preferred to return a different status code like 406 Not Acceptable

[offtherailz]

I suggest to return the same error of the other restriction rules fails:
HTTP Status 403 - Request Type is not among the ones allowed for this proxy e.g.