Entity/Shipment.php
public function addShipmentElement(ShipmentElement $shipmentElements)
    {
        $this->shipmentElements[] = $shipmentElements;
        $shipmentElements->setShipment($this);

        return $this;
    }
public function addShipmentElement(ShipmentElement $shipmentElements)
    {
        $this->shipmentElements[] = $shipmentElements;
        $shipmentElements->setShipment($this);

        return $this;
    }
Add shipmentElements

@param ShipmentElement $shipmentElements

@return Shipment