Wordpress NAV Walker not showing

[admin]

I have a custom wordpress theme and I implemented a custom walker for the nav

In my functions.php, I have this code

class My_Walker extends Walker_Nav_Menu
    {
        function start_el(&$output, $item, $depth, $args) {
            global $wp_query;
            $indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';

            $class_names = $value = '';

            $classes = empty( $item->classes ) ? array() : (array) $item->classes;

            $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) );
            $class_names = ' class="' . esc_attr( $class_names ) . '"';

            $output .= $indent . '<li id="menu-item-'. $item->ID . '"' . $value . $class_names .'>';

            $attributes  = ! empty( $item->attr_title ) ? ' title="'  . esc_attr( $item->attr_title ) .'"' : '';
            $attributes .= ! empty( $item->target )     ? ' target="' . esc_attr( $item->target     ) .'"' : '';
            $attributes .= ! empty( $item->xfn )        ? ' rel="'    . esc_attr( $item->xfn        ) .'"' : '';
            $attributes .= ! empty( $item->url )        ? ' href="'   . esc_attr( $item->url        ) .'"' : '';

            $item_output = $args->before;
            $item_output .= '<a'. $attributes .'>';
            $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
            $item_output .= '<br /><span class="sub">' . $item->description . '</span>';
            $item_output .= '</a>';
            $item_output .= $args->after;

            $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
        }
    }

and in my header.php

<div id="access">
    <?php
    wp_nav_menu( array(
        'theme_location' => 'primary',
         'walker'=> new My_Walker
    ));
    ?>
</div>

but when I view my page source, there is no data in the elements

<div id="access">
            <div class="menu"><ul><li id="menu-item-5" class=""><a><br /><span class="sub"></span></a></li><li id="menu-item-8" class=""><a><br /><span class="sub"></span></a></li><li id="menu-item-10" class=""><a><br /><span class="sub"></span></a></li><li id="menu-item-13" class=""><a><br /><span class="sub"></span></a></li><li id="menu-item-15" class=""><a><br /><span class="sub"></span></a></li><li id="menu-item-17" class=""><a><br /><span class="sub"></span></a></li></ul></div>
        </div>

this is suppose to be a simple walker, but I don't get it to work