how extends Walker_Nav_Menu without Undefined property: stdClass:: warnings

Hi
I’m have extanded Walker_Nav_Menu here is the 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 ) .'”‘ : ”;

$prepend = ”;
$append = ”;
$description = ! empty( $item->description ) ? ‘<p>’.esc_attr( $item->description ).'</p>’ : ”;

if($depth != 0)
{
$description = $append = $prepend = “”;
}

$item_output = $args->before;
$item_output .= ‘<a’. $attributes .’>’;
$item_output .= $args->link_before .$prepend.apply_filters( ‘the_title’, $item->title, $item->ID ).$append;
$item_output .= $description.$args->link_after;
$item_output .= ”;
$item_output .= $args->after;

$output .= apply_filters( ‘walker_nav_menu_start_el’, $item_output, $item, $depth, $args );

}
}

but if from the admin the menu is not created and selected I’m getting a list of worning, after when I’ve selected the primary menu all wornings disappear.
please help how I can solve this and show result without warning even if the primary menu is not selected

thanks