Update app.py

app.py

@@ -100,6 +100,10 @@ def create_retriever_from_chroma(vectorstore_path="docs/chroma/", search_type='m
 
 def main():
 
+
+    if "messages" not in st.session_state:
+        st.session_state.messages = None
+
     st.set_page_config(page_title="Chat with multiple PDFs",
                        page_icon=":books:")
     st.write(css, unsafe_allow_html=True)