diff --git a/judgelm/llm_judge/common.py b/judgelm/llm_judge/common.py
index c756696..4a4ed1a 100644
--- a/judgelm/llm_judge/common.py
+++ b/judgelm/llm_judge/common.py
@@ -134,7 +134,7 @@ def to_gradio_chatbot(self):
                 ret[-1][-1] = msg
         return ret
 
-    def copy(self, answer_num):
+    def copy(self, answer_num = None):
         if answer_num is not None:
             prompt = self.prompt\
                 .replace("two", num2words[int(answer_num)])\
@@ -294,4 +294,4 @@ def load_questions(question_file: str, begin: Optional[int], end: Optional[int])
     sep_style=SeparatorStyle.SINGLE,
     sep="</s>",
     appendix="### Response:10"
-)
\ No newline at end of file
+)