code: protected function compareStockUnitByEda(StockUnitInterface $u1, StockUnitInterface $u2)
      {
          $u1HasEda = null !== $u1->getEstimatedDateOfArrival();
          $u2HasEda = null !== $u2->getEstimatedDateOfArrival();
  
          if (!$u1HasEda && $u2HasEda) {
              return 1;
          }
          if ($u1HasEda && !$u2HasEda) {
              return -1;
          }
          if ($u1->getEstimatedDateOfArrival() != $u2->getEstimatedDateOfArrival()) {
              return $u1->getEstimatedDateOfArrival() > $u2->getEstimatedDateOfArrival() ? 1 : -1;
          }
  
          return 0;
      }
docs: Compares the units regarding to their estimated date of arrival.
  
  @param StockUnitInterface $u1
  @param StockUnitInterface $u2
  
  @return int