Update app.py

app.py

@@ -150,7 +150,7 @@ def main():
             return vectorstore , conversation
 
 
-    if conversation not None:
+    if conversation is not None:
         st.subheader("Chat Bot")
         if user_question := st.text_input("Ask a question about your documents:"):
             handle_userinput(user_question, vectorstore, conversation)