wp_nav_menu always falls back to a menu

hey all,
i’m writing an automated function that generates a menu from a function. it calls wp_nav_menu on each item from an array, because i want this to be dynamic. the problem is, no matter how i set it, if the menu doesn’t exist, wp_nav_menu is generating a menu, eg the ‘default’. here is my code (items is just a set of strings):

for($i=0;$i<count($items);$i++) {

    $themenu=$items[$i];

    $mymenu = wp_nav_menu(array(
            'menu' => $themenu,
            'menu_class' => 'mymenu',
            'container' => 'false',
            'fallback_cb' => 'false',
            'echo' => false
            )
        );  

    echo $themenu;

    }

i know its partially working, because if $themenu exists, it shows the correct one. but if it doesn’t, it’ll just show any menu! not just annoying, but also actively breaks the user experience.

wp_nav_menu() indeed tries a lot to provide you with a menu, and fallback_cb is only executed when nothing else works. From the code:

• If menu is provided and refers to an existing menu (looked up via wp_get_nav_menu_object(), which accepts an id, slug or name), this will be the menu
• Otherwise, if theme_location is set to a registered menu location, this will be passed to wp_get_nav_menu_object()
• Otherwise, WordPress will search for the first existing menu that has items and use that
• Otherwise, fallback_cb is called, which by default is wp_page_menu, which is a menu of all the pages

So if you only want to use the menu argument, you should test this yourself by calling wp_get_nav_menu_object(). Only if this returns something you should call wp_nav_menu().