Update: this was caused by the fact that i didn't have a menu created in the menu page.
I want to add a class to the ul of wp_nav_menu. I tried this code:
<?php $defaults = array( 'menu_class' => 'menu', 'items_wrap' => '<ul id="%1$s" class="%2$s">%3$s</ul>', ); wp_nav_menu( $defaults ); ?>
According to wordpress codex changing the menu from 'menu_class' => 'menu', should change the class of the ul, but instead it changes the class of the div wrapping the ul.
<div class="this class is changed"><ul><li class="page_item page-item-2"><a href="http://domain.tld/">Sample Page</a></li></ul></div>