diff --git a/rag/llm/chat_model.py b/rag/llm/chat_model.py
index 3612cc55d..48dc29ba0 100644
--- a/rag/llm/chat_model.py
+++ b/rag/llm/chat_model.py
@@ -62,6 +62,8 @@ class Base(ABC):
                 **gen_conf)
             for resp in response:
                 if not resp.choices:continue
+                if not resp.choices[0].delta.content:
+                    resp.choices[0].delta.content = ""  
                 ans += resp.choices[0].delta.content
                 total_tokens = (
                     (