stupid question about menu

Hello I want to remove the div wrapper on the primary menu, by the codex rules the code will be

<?php wp_nav_menu( array('theme_location' => 'primary', 'menu_container' => false) ); ?>

but I get the same structure

<div class="menu">
<ul>
<li>item1</li>
<li>item2</li>
<li>item3</li>
</ul>
</div>