add warning for visitor args
add warning for visitor args

abhishekgahlot/fetchbot,vizewang/fetchbot,PuerkitoBio/fetchbot,suzuken/fetchbot,PuerkitoBio/fetchbot,firebitsbr/fetchbot,dullgiulio/fetchbot,dullgiulio/fetchbot,abhishekgahlot/fetchbot,firebitsbr/fetchbot,vizewang/fetchbot,suzuken/fetchbot