Update app.py

app.py

@@ -16,6 +16,9 @@ with open("kosen.txt", encoding="utf-8") as f:
 def rag_chat(message, history):
     # 過去の会話を文字列化
     conversation = ""
+    if history is None:
+        history = []
+    
     for msg in history:
         role = msg["role"]
         content = msg["content"]