Update app.py

app.py

@@ -79,7 +79,7 @@ if submitted:
             selected_df = pd.DataFrame()
             pass
 
-    if selected_df.isnull():
+    if selected_df is None:
         if len(selected_df) != 0 :
             st.success('Feature vector successfully created.')
             csv = convert_df(selected_df)