private function getStockUnitMapper(EntityManagerInterface $em)
    {
        if (null === $this->stockUnitMapper) {
            $this->stockUnitMapper = new DiscriminatorMapper($em, AbstractStockUnit::class);
        }

        return $this->stockUnitMapper;
    }
private function getStockUnitMapper(EntityManagerInterface $em)
    {
        if (null === $this->stockUnitMapper) {
            $this->stockUnitMapper = new DiscriminatorMapper($em, AbstractStockUnit::class);
        }

        return $this->stockUnitMapper;
    }
Returns the stock unit mapper.

@param EntityManagerInterface $em

@return DiscriminatorMapper