Fatal error: Uncaught Error: Class "WP_Customize_Setting" not found in C:\web_server\htdocs\home\wp-includes\customize\class-wp-customize-background-image-setting.php:17 Stack trace: #0 {main} thrown in C:\web_server\htdocs\home\wp-includes\customize\class-wp-customize-background-image-setting.php on line 17