code: private function respondDefault(&$i, &$results, $parameter)
      {
          $defaultResult = $this->parameterCluster->default->call(
              $this, $parameter
          );
  
          if ($defaultResult === -1) {
              $this->valid = false;
          }
  
          $results[$parameter] = $defaultResult;
          $i++;
      }
docs: Parses the parameter with the default closure and increments
  the parameter parser. If '-1' is returned by the default
  closure, the parameters will be invalidated.
  
  @param  int    &$i
  @param  array  &$results
  @param  string $parameter