commit 9bab0423825ae2aa7bec7fd423bcb646fcc77544 (HEAD, route-filter)
Author: Tim Plunkett <git@plnktt.com>
Date:   Sat Oct 24 12:09:02 2015 -0700

    Reduce amount of running code for empty collections.

diff --git a/src/Routing/VariantRouteFilter.php b/src/Routing/VariantRouteFilter.php
index 922a6b9..684e1e9 100644
--- a/src/Routing/VariantRouteFilter.php
+++ b/src/Routing/VariantRouteFilter.php
@@ -65,16 +65,16 @@ public function applies(Route $route) {
    * {@inheritdoc}
    */
   public function filter(RouteCollection $collection, Request $request) {
-    $new_collection = NULL;
+    // Only proceed if the collection is non-empty.
+    if (!$collection->count()) {
+      return $collection;
+    }
 
     // Store the unaltered request attributes.
     $original_attributes = $request->attributes->all();
+    $this->prepareRequest($collection, $request);
 
-    // Only prepare the request if the collection is non-empty.
-    if ($collection->count()) {
-      $this->prepareRequest($collection, $request);
-    }
-
+    $new_collection = NULL;
     foreach ($collection as $name => $route) {
       /** @var \Symfony\Component\Routing\Route $route */
       $defaults = $route->getDefaults();