Entity/OfferElement.php
public function setProduct(ProductInterface $product)
    {
        $this->product = $product;
        $this->setUnitPrice($product->getPrice());

        $this->calculateTotalPrice();

        return $this;
    }
public function setProduct(ProductInterface $product)
    {
        $this->product = $product;
        $this->setUnitPrice($product->getPrice());

        $this->calculateTotalPrice();

        return $this;
    }
Set product

@param ProductInterface $product

@return OfferElement