code: func ServerInternal(detail string, a ...interface{}) *ProblemDetails {
  	return &ProblemDetails{
  		Type:       ServerInternalProblem,
  		Detail:     fmt.Sprintf(detail, a...),
  		HTTPStatus: http.StatusInternalServerError,
  	}
  }
docs: // ServerInternal returns a ProblemDetails with a ServerInternalProblem and a
  // 500 Internal Server Failure status code.