Docs: Correct `@type` annotation for `WP_Customize_Nav_Menu_Item_Setting::$value`.

Props diddledan.
Fixes #46853.

git-svn-id: https://develop.svn.wordpress.org/trunk@45427 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php

@@ -84,7 +84,7 @@ class WP_Customize_Nav_Menu_Item_Setting extends WP_Customize_Setting {
 	 * Storage of pre-setup menu item to prevent wasted calls to wp_setup_nav_menu_item().
 	 *
 	 * @since 4.3.0
-	 * @var array
+	 * @var array|null
 	 */
 	protected $value;