[AsseticBundle] coding standard and comment tweaks

src/Symfony/Component/HttpKernel/Bundle/Bundle.php

@@ -69,7 +69,9 @@ abstract class Bundle extends ContainerAware implements BundleInterface
             $this->extension = class_exists($class) ? new $class() : false;
         }
 
-        return $this->extension ?: null;
+        if ($this->extension) {
+            return $this->extension;
+        }
     }
 
     /**

src/Symfony/Component/HttpKernel/Bundle/BundleInterface.php

@@ -42,7 +42,7 @@ interface BundleInterface
     /**
      * Returns the container extension that should be implicitly loaded.
      *
-     * @return ExtensionInterface|null The default extension
+     * @return ExtensionInterface|null The default extension or null if there is none
      */
     function getContainerExtension();