code: func Malformed(detail string, a ...interface{}) *ProblemDetails {
  	return &ProblemDetails{
  		Type:       MalformedProblem,
  		Detail:     fmt.Sprintf(detail, a...),
  		HTTPStatus: http.StatusBadRequest,
  	}
  }
docs: // Malformed returns a ProblemDetails with a MalformedProblem and a 400 Bad
  // Request status code.