fix: route null pointer

lib/src/fluro_router.dart

@@ -126,7 +126,7 @@ class FluroRouter {
     AppRouteMatch match = _routeTree.matchRoute(path);
     AppRoute route = match?.route;
 
-    if (route.transitionDuration != null) {
+    if (route?.transitionDuration != null) {
       transitionDuration = route.transitionDuration;
     }