Update app.py

app.py

@@ -84,7 +84,7 @@ def history2messages(history: List[Dict]) -> List[Dict]:
         if "content" not in cur_message:
             cur_message["content"] = dict()
 
-        if "metadata" not in item:
+        if "metadata" not in item or item["metadata"] is None:
             item["metadata"] = {"title": None}
         if item["metadata"]["title"] is None:
             cur_message["content"]["text"] = item["content"]