diff --git a/metagpt/memory/brain_memory.py b/metagpt/memory/brain_memory.py
index 422c096f3..9d1b038bb 100644
--- a/metagpt/memory/brain_memory.py
+++ b/metagpt/memory/brain_memory.py
@@ -53,6 +53,6 @@ class BrainMemory(pydantic.BaseModel):
     @property
     def last_talk(self):
         if len(self.history) == 0 or not self.history[-1].is_contain_tags([MessageType.Talk.value]):
-            return ""
+            return None
         return self.history[-1].content
 
diff --git a/metagpt/roles/assistant.py b/metagpt/roles/assistant.py
index 3924039b5..1e503857a 100644
--- a/metagpt/roles/assistant.py
+++ b/metagpt/roles/assistant.py
@@ -113,6 +113,8 @@ class Assistant(Role):
     async def refine_memory(self) -> str:
         history_text = self.memory.history_text
         last_talk = self.memory.last_talk
+        if last_talk is None:  # No user feedback, unsure if past conversation is finished.
+            return None
         if history_text == "":
             return last_talk
         history_summary = await self._llm.get_context_title(history_text, max_words=20)