private function getUnitOfVariation(array $variation)
    {
        foreach (self::$units as $unit) {
            if ((int) $unit['id'] === (int) $variation['unit']['unitId']) {
                return $unit['unitOfMeasurement'];
            }
        }

        return null;
    }
private function getUnitOfVariation(array $variation)
    {
        foreach (self::$units as $unit) {
            if ((int) $unit['id'] === (int) $variation['unit']['unitId']) {
                return $unit['unitOfMeasurement'];
            }
        }

        return null;
    }
@param array $variation

@return null|string