Update app.py

app.py

@@ -578,7 +578,7 @@ async(c, o, p, d, n, m, s)=>{
             now = new Date().getTime();
             delta = now - then;
             then = now - (delta % interval);
-            if (delta >= interval - tolerance) {
+            if (delta >= interval - tolerance && BABYLON.Engine.LastCreatedScene.activeCamera) {
                 BABYLON.Engine.LastCreatedScene.activeCamera.target = BABYLON.Engine.LastCreatedScene.activeCamera.getDirection(parallax);
                 BABYLON.Engine.LastCreatedScene.render();
             }