Update app.py

app.py

@@ -78,6 +78,9 @@ detector.prepare(-1, nms_thresh=0.5, input_size=(640, 640))
 
 
 def detect(image: np.ndarray) -> tuple[Image.Image, list[Image.Image]]:
+    if image is None:
+        return None, []
+
     image = image[:, :, ::-1]  # RGB -> BGR
     bboxes, vbboxes = detect_person(image, detector)
     res = visualize(image, bboxes, vbboxes)