action="" should give error
Empty action (action, action="") is invalid HTML and should give error.
<form method="post" action=""> </form>
Test on https://validator.w3.org
Action must be a valid URL, but empty is not a valid URL: https://html.spec.whatwg.org/multipage/forms.html#the-form-element In this case, just leave action out. (I know most browsers handle it as if it weren't there, it's just about exactness)