[ADP-402] Empty Problem Type

According to https://www.rfc-editor.org/rfc/rfc7807#section-4.2, if you don’t need extra information to expand the original HTTP status code, you could use about:blank.

Guidance

MAY use about:blank if you don’t need extra information to expand the original HTTP status code.
You MAY specify the type as status code reflected text even you don't have the plan to publish the problem type to the public network.

Example

Both of the following work:

http

HTTP/1.1 404 Not Found
Content-Type: application/problem+json
Content-Language: en

{
  "type": "about:blank",
  "title": "Not Found",
  "status": 404,
  "detail": "The requested resource could not be found on this server."
}

http

HTTP/1.1 404 Not Found
Content-Type: application/problem+json
Content-Language: en

{
  "type": "/problems/not-found",
  "title": "Not Found",
  "status": 404,
  "detail": "The requested resource could not be found on this server."
}