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// Register Custom Navigation Walker
require_once get_template_directory() . '/nav-walker/class-wp-bootstrap-navwalker.php';

<nav class="nav-primary d-none {!! $mobile_breakpoint !!}">
    @if (has_nav_menu('primary_navigation'))
      {!! wp_nav_menu([
        'theme_location'  => 'primary_navigation',
        'depth'           => 2,
        'menu_class'      => 'nav',
        'fallback_cb'     => 'WP_Bootstrap_Navwalker::fallback',
        'walker'          => new WP_Bootstrap_Navwalker(),
      ]) !!}
    @endif
  </nav>