Why does $request->get('_route') return null in Symfony 2?

Question

PHP

Applied the following listener

<?php
namespace Acme\HelloBundle\EventListener;

use Symfony\Component\HttpKernel\Event\GetResponseEvent;

class AddressListener
{
    public function onKernelRequest(GetResponseEvent $event)
    {
        $request = $event->getRequest();
        $routeName = $request->get('_route');
        var_dump($routeName);
    }
}

I have about 10 routes used in the project. var_dump shows normally the names of all routes, except for one. It comes out null for some reason, although the route itself is processed normally, as expected. What could be the problem?
The route itself

address:
    path: /address/
    defaults: { _controller: AcmeHelloBundle:Address:index }
    requirements:
        _method: GET

Listener Service

kernel.listener.address:
    class: Acme\HelloBundle\EventListener\AddressListener
    tags:
        - { name: kernel.event_listener, event: kernel.request, method: onKernelRequest }

I'm using Symfony 2.5