Common/Model/Notify.php
public function addShipment(ShipmentInterface $shipment)
    {
        if (!$this->shipments->contains($shipment)) {
            $this->shipments->add($shipment);
        }

        return $this;
    }
public function addShipment(ShipmentInterface $shipment)
    {
        if (!$this->shipments->contains($shipment)) {
            $this->shipments->add($shipment);
        }

        return $this;
    }
Adds the shipment.

@param ShipmentInterface $shipment

@return Notify