code: func BoolValueOrDefault(r *http.Request, k string, d bool) bool {
  	if _, ok := r.Form[k]; !ok {
  		return d
  	}
  	return BoolValue(r, k)
  }
docs: // BoolValueOrDefault returns the default bool passed if the query param is
  // missing, otherwise it's just a proxy to boolValue above.