diff -Naur wp-admin/includes/class-wp-upgrader-skin.php wp-admin/includes/class-wp-upgrader-skin.php
--- wp-admin/includes/class-wp-upgrader-skin.php	2017-07-27 00:40:44.000000000 +0530
+++ wp-admin/includes/class-wp-upgrader-skin.php	2018-12-11 11:54:28.638482661 +0530
@@ -15,8 +15,22 @@
  */
 class WP_Upgrader_Skin {
 
+	/**
+	 *
+	 * @var WP_Upgrader instance $upgrader
+	 */
 	public $upgrader;
+
+	/**
+	 *
+	 * @var bool $done_header
+	 */
 	public $done_header = false;
+
+	/**
+	 *
+	 * @var bool $done_footer
+	 */
 	public $done_footer = false;
 
 	/**
@@ -26,6 +40,11 @@
 	 * @var string|bool|WP_Error
 	 */
 	public $result = false;
+
+	/**
+	 *
+	 * @var array $options
+	 */
 	public $options = array();
 
 	/**