MUST specify default response

Each operation MUST include a default error response that combines multiple errors.

Invalid Example

The example below contains only a 200 response.

responses:
   ...
get:
  summary: Get User Info by User ID
   tags: []
   responses:
     '200':
       description: OK

Valid Example

The example below contains a 200 response and a default response that references the Problem errors file.

responses:
   ...
get:
  summary: Get User Info by User ID
   tags: []
   responses:
     '200':
       description: OK
     default:
       description: User Not Found
       content:
         application/problem+json:
           schema:
             $ref: ../models/Problem.yaml

Zalando Guideline 151