Update app.py

app.py

@@ -77,7 +77,7 @@ def add_title(img_bgr, title):
     return np.vstack([bar, img_bgr])
 
 def parse_xml_roi_points(xml_path):
-    """Parse your XML structure, return list of polygons (Nx2 points)."""
+    """Parse XML, return list of polygons (Nx2 points)."""
     polys = []
     try:
         tree = ET.parse(xml_path)
@@ -165,8 +165,11 @@ def homography_all_detectors(flat_file, persp_file, json_file, xml_file):
         results.append((cv2.cvtColor(composite, cv2.COLOR_BGR2RGB), f"{method} Grid"))
         download_files.append(file_name)
 
-    while len(download_files)<5: download_files.append(None)
-    return [results]+download_files[:5]
+    # pad list with "" instead of None (to avoid Gradio error)
+    while len(download_files) < 5:
+        download_files.append("")
+
+    return [results] + download_files[:5]
 
 # ---------------- Gradio UI ----------------
 iface = gr.Interface(