null_values.xml

<?xml version="1.0" encoding="UTF-8" ?>
<routes xmlns="http://symfony.com/schema/routing"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/routing https://symfony.com/schema/routing/routing-1.0.xsd">

    <route id="blog_show" path="/blog/{slug}">
        <default key="foo" xsi:nil="true" />
        <default key="bar" xsi:nil="1" />
        <default key="foobar" xsi:nil="false">foo</default>
        <default key="baz" xsi:nil="0">bar</default>
    </route>
</routes>