Class duplicate validation error fix

[asifpix]

Now this walker will output class only once.

[AlexWebLab]

how about to replace this:
$item_output .= ($depth > 0) ? '<a' . $attributes . '>' : '<a' . $attributes . '>';
with this:
$item_output .= '<a' . $attributes . '>';

[AlexWebLab]

I've also replaced this:
$nav_link_class = ( $depth > 0 ) ? 'dropdown-item nav-link ' : 'nav-link ';
with this:
$nav_link_class = ( $depth > 0 ) ? 'dropdown-item ' : 'nav-link ';
because, according to the official documentation, when an anchor tag is grandchild of a .dropdown-menu class then it has only .dropdown-item class and not .nav-link class.

[asifpix]

Thanks for the fix. I am removing the fork.