wp_nav_menu not rendering menu_class correctly

Here is my code in the header

<nav class="col-md-9" role="navigation">
  <?php wp_nav_menu(
    array(
      'theme_location'  => 'navigation',
      'menu'            => '',
      'container'       => false,
      'container_class' => 'menu-{menu slug}-container',
      'container_id'    => '',
      'menu_class'      => 'nav nav-pills',
      'menu_id'         => 'menu-{menu slug}',
      'echo'            => true,
      'fallback_cb'     => 'wp_page_menu',
      'before'          => '',
      'after'           => '',
      'link_before'     => '',
      'link_after'      => '',
      'items_wrap'      => '<ul id="%1$s" class="%2$s">%3$s</ul>',
      'depth'           => 0,
      'walker'          => ''
    )
  );
?>
</nav>

and this renders me

<nav class="col-md-9" role="navigation">
  <div class="nav nav-pills">
    <ul>
      <li class="page_item page-item-1791 current_page_item"><a href="https://retesz.w.pw/biografia/">Biográfia</a></li>
      <li class="page_item page-item-1783"><a href="https://retesz.w.pw/">F?oldal</a></li>
    </ul>
  </div>
</nav>

From what I read in the codex:

$menu_class
(string) (optional) The class that is applied to the ul element which encloses the menu items. Multiple classes can be separated with spaces. Formerly known as $wrap_class.
Default: menu

It’s supposed to apply the class nav nav-pills to the ul, not the container div, especially because I turned off the container with 'container' => false.

Can someone explain what I’m doing wrong.

Any help is appreciated.