Confusing and undocumented if statement in route subscriber

[pfrenssen]

While reviewing #85 I found a dubious section of code in RouteSubscriber::alterRoutes() and no comments are given on why this is needed:

    // Replace the core register route controller.
    $route = $collection->get('user.register');
    if ($route instanceof Route) {
      // ...
    }

Why is it here assumed that RouteCollection::get() would return objects which are not Route objects? If this can happen, why would we ignore this silently?

I see from the definition of \Symfony\Component\Routing\RouteCollection::get() that it only returns Route or NULL:

    /**
     * Gets a route by name.
     *
     * @param string $name The route name
     *
     * @return Route|null A Route instance or null when not found
     */
    public function get($name);

I'm not sure if something came up during testing that necessitated this if statement, but it seems more likely that this is just a mistake and the if statement can be simply removed. If is is necessary then we should have some clear documentation on why this can happen, and a test to prove that we handle the case correctly.

Ref. https://github.com/openeuropa/oe_authentication/blame/master/src/Routing/RouteSubscriber.php#L37

This entire class could use an overhaul by the way, there is almost no documentation, except for some comments that explain what the code is doing, but not why.