Wordpress custom walker menu doesnt' display items - wordpress

Question

I'm working with the custom menu Walker class but have troubles on displaying menu items.
The only menu item which's displayed is the "home" item.
I created two pages but I just get void link tags.
Plus the "home" menu item doesn't get the "hvr-bounce-to-top" class and I would like all the items to get that class.
This is the result I get checking firebug:
<div class="nav-menu">
<ul>
<li class="current_page_item">
Home
</li>
<li id="menu-item-4" class=" hvr-bounce-to-top ">
<a></a>
</li>
<li id="menu-item-2" class=" hvr-bounce-to-top ">
<a></a>
</li>
</ul>
</div>
This is the wp_nav_menu code in header.php:
<?php wp_nav_menu( array(
'theme_location' => 'primary',
'menu_class' => 'nav-menu',
'container' => false,
'echo' => true,
'before' => '',
'after' => '',
'link_before' => '',
'link_after' => '',
'depth' => 0,
'walker' => new DescriptionWalker()
) );//wp_nav_menu
?>
And this is my Walker class in the function.php theme directory:
class DescriptionWalker extends Walker_Nav_Menu
{
function start_el(&$output, $item, $depth, $args)
{
global $wp_query;
echo 'title = ' . $item->title;
$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 ) . ' hvr-bounce-to-top "';
$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 );
$item_output .= $args->link_after;
$item_output .= '</a>';
$item_output .= $args->after;
$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
}
}//DescriptionWalker
Thank you