在升级到Wordpress 4.8之前，我可以在wp_nav_menu(). 我有几个网站运行4.7.5，代码正常。升级下面的代码后，什么都没做。

    <?php
    $args = array(
         \'theme_location\'  => $nav_name,
         \'container\'  => \'nav\',
         \'items_wrap\' => \'<ul>%3$s</ul>\',
         \'container_class\' => " ",
         \'echo\' => false
    );
    $nav = wp_nav_menu( $args );
    $nav = str_replace(\'<ul class="sub-menu">\', \'<div class="mobile-drop"><ul>\', $nav);
    $match = \'</ul>\'."\\n".\'</li>\';
    $nav = str_replace($match, \'</ul></div></li>\', $nav);
    echo $nav;
    ?>