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)