suppress error when deleting an image

app.py

@@ -77,6 +77,9 @@ def image_changed(image):
   json = estimate_body(image)
   return json, image.width, image.height
 
+def image_preprocess(image):
+  return image is not None
+
 html_text = f"""
     <canvas id="canvas" width="512" height="512"></canvas>
     <script type="text/javascript" defer>{file_contents}</script>
@@ -97,6 +100,7 @@ with gr.Blocks() as demo:
 
   source.change(
     fn = image_changed,
+    preprocess = image_preprocess,
     inputs = [source],
     outputs = [json, width, height])
   startBtn.click(