Index: src/wp-admin/includes/template.php
===================================================================
--- src/wp-admin/includes/template.php	(revision 38412)
+++ src/wp-admin/includes/template.php	(working copy)
@@ -1989,7 +1989,7 @@
  * @return WP_Screen Screen object.
  */
 function convert_to_screen( $hook_name ) {
-	if ( ! class_exists( 'WP_Screen', false ) ) {
+	if ( ! class_exists( 'WP_Screen' ) ) {
 		_doing_it_wrong( 'convert_to_screen(), add_meta_box()', __( "Likely direct inclusion of wp-admin/includes/template.php in order to use add_meta_box(). This is very wrong. Hook the add_meta_box() call into the add_meta_boxes action instead." ), '3.3.0' );
 		return (object) array( 'id' => '_invalid', 'base' => '_are_belong_to_us' );
 	}