Filters post in admin with dropdown select, custom post type

Thank you so much, it’s working. Here is my modified code:

function wpse45436_posts_filter( $query ){
    global $pagenow;
    $type="post";
    if (isset($_GET['post_type'])) {
        $type = $_GET['post_type'];
    }
    if ( 
        'post' == $type  
         && is_admin()  
         && $pagenow =='edit.php'  
         && isset($_GET['ADMIN_FILTER_FIELD_VALUE']) 
         && $_GET['ADMIN_FILTER_FIELD_VALUE'] != '' 
         && $query->is_main_query()
     ) {
            $query->query_vars['meta_key'] = 'n_de_ldition';
            $query->query_vars['meta_value'] = $_GET['ADMIN_FILTER_FIELD_VALUE'];
        }
    }

By targetting the main query with $query->is_main_query() we avoid modifying our get_posts() call that we use to populate the select box. The reason is that get_posts() is just a wrapper for the WP_Query so the parse_query hook can affect it as well.