Nginx valid_referers with "none" option disable hotlinking protection

This is my code:

valid_referers none blocked *.alloweddomain.com;
if ($invalid_referer){
return 403;
}
}

The hotlinking doesnt work. But this works fine:

valid_referers blocked *.alloweddomain.com;
if ($invalid_referer){
return 403;
}
}

Why **none** option cause the code not work?

Reference: http://nginxlibrary.com/hotlink-protection/