Initialized the session object to None

app.py

@@ -101,7 +101,10 @@ def main():
 
     if "conversation" not in st.session_state:
         index = load_embeddings_and_index()
-        st.session_state.conversation = get_conversation_chain(index)
+        if index==None:
+            st.session_state.conversation = None
+        else:
+            st.session_state.conversation = get_conversation_chain(index)
     if "chat_history" not in st.session_state:
         st.session_state.chat_history = None