Update app.py

app.py

@@ -140,7 +140,9 @@ class ToDictListEncoder(JSONEncoder):
 
     def default(self, o):
         """Encode to JSON using to_dict."""
-        return [res.to_dict() for res in o]
+        if o:
+            return o.to_dict()
+        return []
 
 
 if st_return_decision_process: