How to use optional ParamConverter with null default in Route in Symfony Controller

CalculationController.php

<?php

namespace Sps\Bundle\CalculationBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\ParamConverter;

class CalculationController extends Controller
{
    /**
     * @Route("/calculation/dormer/calculate/{priceQuoteId}", defaults={"priceQuoteId" = null})
     * @ParamConverter("priceQuoteRequest", isOptional="true", class="SpsPriceQuoteBundle:PriceQuoteRequest", options={"id" = "priceQuoteId"})
     * @Template()
     * @Security("has_role('ROLE_DOMO_CALCULATION_DORMER')")
     */
    public function createAction(PriceQuoteRequest $priceQuoteRequest = null)
    {
    }
}

in php7.2 and symfony 4.3 its as simple as

class CalculationController extends Controller
{
    /**
     * @Route("/calculation/dormer/calculate/{priceQuoteId}")
     * @ParamConverter("priceQuoteRequest", class="SpsPriceQuoteBundle:PriceQuoteRequest", options={"id" = "priceQuoteId"})
     * @Template()
     * @Security("has_role('ROLE_DOMO_CALCULATION_DORMER')")
     */
    public function createAction(?PriceQuoteRequest $priceQuoteRequest)
    {
    }

no defaults in Route, no isOptional="true", no = null in function definition. Simply ?PriceQuoteRequest