code: public function onInitialize(ResourceEventInterface $event)
      {
          $order = $this->getSupplierOrderFromEvent($event);
  
          if (null !== $supplier = $order->getSupplier()) {
              if ($order->getCurrency() !== $supplier->getCurrency()) {
                  $order->setCurrency($supplier->getCurrency());
              }
              if (null === $order->getCarrier()) {
                  $order->setCarrier($supplier->getCarrier());
              }
          }
      }
docs: Initialize event handler.
  
  @param ResourceEventInterface $event