Update app.py

app.py

@@ -668,13 +668,17 @@ def set_tools() -> List[Tool]:
     # python_repl = PythonREPLTool()
 
     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
     }
 
+    if st.session_state.retriever_tool:
+        tool_dictionary["Retrieval"] = st.session_state.retriever_tool
+
+
     if st.session_state.bing_subscription_validity:
         search = BingSearchAPIWrapper()
     elif st.session_state.google_cse_id_validity: