Laravel 5.4 required_with doesn't works with alpha_dash and min

That's my validation code:

'old_password' => 'max:255|required_with:new_password|old_password',
'new_password' => 'max:255|required_with:old_password|min:6|alpha_dash',

I've got alpha_dash and min:6 validation fails if both fields is empty. How can I fix it?

old_password is a custom rule

Validator::extend('old_password', function ($attribute, $value, $parameters, $validator) {
  if( $value == ''){
      return true;
  } else {
      return \Hash::check($value, request()->user()->password);
  }
});

via fiter