a.php

function postStartNegotiations1(Property $property, Offer $offer)
{
        return $this->get('app.command.add_offer')->execute((object) [
            'suggestedPrice' => $offer->getSuggestedPrice(),
            'buyer' => $this->getUser(),
            'advert' => $advert
        ]);
}

function postStartNegotiations2(Property $property, Offer $offer)
{
        return $advert->startNegotiations(
                $this->getUser(), $offer->getSuggestedPrice()
        );
}