code: private function push(array &$list, $oid, StockUnitInterface $unit)
      {
          if (!$this->has($list, $oid, $unit)) {
              $list[$oid][] = $unit;
          }
      }
docs: Pushes the unit to the given list for the given object identifier.
  
  @param array              $list
  @param string             $oid
  @param StockUnitInterface $unit