WordPress Database Error Column ‘type2’ cannot be null

Hi. Your plugin is nice. But sometimes result in a database error in my apache error.log. One example is shown below:

WordPress Database Error Column ‘type2’ cannot be null for query REPLACE INTO dbprefix_wpss_links (url, type, type2, id) VALUES (‘/2008/04/560/article-slug-example/feed/’, ‘singular’, NULL, NULL) made by require(‘wp-blog-header.php’), require_once(‘wp-includes/template-loader.php’), do_action(‘template_redirect’), call_user_func_array, wpss_footer