Update app.py

app.py

@@ -160,7 +160,7 @@ def main():
     if "conversation" not in st.session_state:
         st.session_state.conversation = None
     if "chat_history" not in st.session_state:
-        st.session_state.chat_history = None
+        st.session_state.chat_history = []
     if "vectorstore" not in st.session_state: #Store vectorstore in session state
         st.session_state.vectorstore = None