Wordpress Custom Walker li id to li class

I'm currently using a WordPress custom Walker to customize my navigation. It currently generates this navigation:

<nav class="nav-top clearfix">
<ul class="clearfix">
<li id="menu-item-69" class="current_page_item"><a href="#">test1</a></li>
<li id="menu-item-68"><a href="#">test2</a></li>
<li id="menu-item-67"><a href="#">test3</a></li>
<li id="menu-item-66"><a href="#">test4</a></li>
<li id="menu-item-65"><a href="#">test5</a></li>
<li id="menu-item-64"><a href="#">test6</a></li>
</ul>
</nav>

When i click on test2, it will apply the current_page_item class to it.

Everything is working fine, however I also want to use the same navigation in the footer. If I do that, then i get validation errors because of the li id. How do i change the li id to li class ?

Here's my custom Walker:

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;

       $current_indicators = array('current_page_item');

       $newClasses = array();

       foreach($classes as $el){
           //check if it's indicating the current page, otherwise we don't need the class
           if (in_array($el, $current_indicators)){ 
               array_push($newClasses, $el);
           }
       }

       $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $newClasses), $item ) );
       if($class_names!='') $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        ) .'"' : '';

       if($depth != 0)
       {
           //children stuff, maybe you'd like to store the submenu's somewhere?
       }

       $item_output = $args->before;
       $item_output .= '<a'. $attributes .'>';
       $item_output .= $args->link_before .apply_filters( 'the_title', $item->title, $item->ID );
       $item_output .= '</a>';
       $item_output .= $args->after;

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

In case you haven't figured that out yet, here's what you should do:

Replace $newClasses = array(); with:

$newClasses = array( 'menu-item-'. $item->ID );

Then replace the following line:

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

With:

$output .= $indent . '<li' . $value . $class_names .'>';