search only active / running auctions

add_filter('woocommerce_product_query','custom_pre_get_posts' ,99,2 );

function custom_pre_get_posts($q){
    if ( ! is_admin() && $q->is_main_query() && $q->is_search() && isset ( $q->query['only_active_auctions']) ){

        $metaquery = $q->get('meta_query');
        $metaquery []=
                    array(

                        'key' => '_auction_started',
                        'compare'=> 'NOT EXISTS',

                        );
        $metaquery []=
                    array(

                        'key' => '_auction_closed',
                        'compare'=> 'NOT EXISTS'
                        );
        $q->set( 'meta_query', $metaquery );

        return;
    }
    return;
}