secure get_tts_message func

app.py

@@ -117,10 +117,12 @@ def get_tts_message(intent_result):
     Determine the TTS message based on the classification result.
     Reservation intent returns one message; all others, another.
     """
-    if "訂位意圖" in intent_result and "無" not in intent_result:
+    if intent_result and "訂位意圖" in intent_result and "無" not in intent_result:
         return "稍後您將會從簡訊收到訂位連結"
-    else:
+    elif intent_result:
         return "我們將會將您的回饋傳達給負責人，謝謝您"
+    else:
+        return "未能判斷意圖"
 
 def play_tts_message(message, voice='af_heart'):
     """