Update tokenization_minicpm.py

tokenization_minicpm.py

@@ -366,7 +366,7 @@ func2(params)
         tools_string = ""
 
     if add_to_system:
-        if len(messages) > 0 and messages[0]["role"] != "system":
+        if len(messages) > 0 and messages[0]["role"] != "system" and tools_string != "":
             messages.insert(0, {"role": "system", "content": ""})
         return [message_format(msg, system_suffix=tools_string, user_prefix="") for msg in messages]
     else: