Update app.py

app.py

@@ -670,14 +670,12 @@ def set_tools() -> List[Tool]:
     tool_options = ["ArXiv", "Wikipedia", "Python_REPL", "Retrieval"]
 
     tool_dictionary = {
-    "ArXiv": arxiv,
-    "Wikipedia": wikipedia,
-    "Python_REPL": python_repl,
-    "Retrieval": st.session_state.retriever_tool
+        "ArXiv": arxiv,
+        "Wikipedia": wikipedia,
+        "Python_REPL": python_repl,
+        "Retrieval": st.session_state.retriever_tool if st.session_state.retriever_tool else None
     }
 
-
-
     if st.session_state.bing_subscription_validity:
         search = BingSearchAPIWrapper()
     elif st.session_state.google_cse_id_validity: