Removing a to one relationship using PATCH as to the spec errors out

[PieterJanVdb]

Removing a relationship using PATCH as the spec defines here returns the following error:

"errors": [
  {
    "status": "403",
    "code": "EFORBIDDEN",
    "title": "Request validation failed",
    "detail": "Missing \"data\" - have you sent the right http headers?"
  }
]

This happens because for this route, it checks if the data property of the body is either an object or an array, and errors out otherwise.

However the spec specifies that you can unset a relationship by setting data to null like so:

PATCH /articles/1/relationships/author HTTP/1.1
Content-Type: application/vnd.api+json
Accept: application/vnd.api+json

{
  "data": null
}

Is this something that warrants a PR or will no route accept null as the value of data as a rule?