diff --git a/plugin.php src/wp-admin/includes/plugin.php
index 7e660f0..5b04a32 100755
--- a/plugin.php
+++ src/wp-admin/includes/plugin.php
@@ -1609,6 +1609,8 @@ function menu_page_url( $menu_slug, $echo = true ) {
  * @global array $_wp_real_parent_file
  * @global array $_wp_menu_nopriv
  * @global array $_wp_submenu_nopriv
+ *
+ * @return string Default empty. Returns the parent page of current admin page.
  */
 function get_admin_page_parent( $parent = '' ) {
 	global $parent_file, $menu, $submenu, $pagenow, $typenow,
@@ -1669,7 +1671,7 @@ function get_admin_page_parent( $parent = '' ) {
 	if ( empty( $parent_file ) ) {
 		$parent_file = '';
 	}
-	return '';
+	return $parent_file;
 }
 
 /**