Custom Menu not functioning properly

Question

I register 2 menus in my functions.php file:

register_nav_menus(array(
    'main_menu' => 'Main Menu',
    'bottom_menu' => 'Bottom Menu'
));

I populate a menu in the admin and assign the theme location:

I call the menu in my theme:

<?php
    wp_nav_menu('menu', 'main_menu');
?>

After doing all this, bottom_menu is the menu showing up in my theme instead.

Can anyone tell me what I'm doing wrong? Either I'm missing something really silly here or Wordpress is giving me the finger.

Answer 1

By specifying a theme_location argument in my array, the issue was fixed:

wp_nav_menu(array(
    'theme_location' => 'main_menu'
));

Edit

For a distributed Theme, do not pass the 'menu' parameter to the wp_nav_menu() call. It will look for a specific slug of a user-created menu, and will override 'theme_location'. Only ever pass 'theme_location'.