/**
  * fix a php notice for mission services in $b
  *
  * @param array $a
  * @param array $b
  *
  * @return array
  */
 protected function mergeData(array $a, array $b)
 {
     if (isset($b['services']) === false) {
         return $b + $a;
     }
     return parent::mergeData($a, $b);
 }