WordPress how to add <span> after main navigation dropdown

I like to add an empty 'span' in the main navigation li element which has a specific class.

Here is the desired look:

<ul>
<li class="menu-item"><a href="#" class="nav-link"></a></li>
<li class="menu-item"><a href="#" class="nav-link"></a></li>
<li class="menu-item has-childern"><a href="#" class="nav-link"></a><span></span></li>
</ul>

I have a code that adds the span after every nav link:

add_filter('nav_menu_item_args', function ($args, $item, $depth) {
if ( $args -> theme_location == 'primary') {
    $args -> link_after  = '<span></span>';
}
    return $args;
}, 10, 3);

How can I achieve to add the 'span' only in the 'li' element which has the 'has-children' class? Thank you for the help!

You could use nav_menu_link_attributes filter hook to get access to the nav attributes.

From Documentation
nav_menu_link_attributes

• 'after'
  (string) Text after the link markup.
• 'link_after'
  (string) Text after the link text.

So you could set it up in multiple ways, for example you could do something like this:

add_filter('nav_menu_link_attributes', 'your_theme_custom_html_element', 10, 3);

function your_theme_custom_html_element($atts, $item, $args)
{

  if ($args->theme_location == 'primary' && (strpos($atts['class'], 'has-childern') !== false)) {

    $args->after  = '<span></span>';

  }

  return $atts;
}

Just tested on my own website and it works seamlessly fine!