[ADP-402] Empty Problem Type

According to RFC 9457/7807, while the specification allows type: about:blank when no extra information is needed, for client predictability and consistency, this ADP explicitly recommends: Never use about:blank. Always use a concrete, meaningful URI (such as /problems/not-found) for the type field.

Guidance

• SHOULD NOT use about:blank as the type. Even if only conveying HTTP status semantics, always use a concrete URI (e.g. /problems/not-found).

Example

Both of the following work:

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/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."
}

Changelog

• 2025.05.09: Update guidance to be more explicit