--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/customize/class-wp-customize-background-image-setting.php	Mon Oct 14 17:39:30 2019 +0200
@@ -0,0 +1,28 @@
+<?php
+/**
+ * Customize API: WP_Customize_Background_Image_Setting class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customizer Background Image Setting class.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Setting
+ */
+final class WP_Customize_Background_Image_Setting extends WP_Customize_Setting {
+	public $id = 'background_image_thumb';
+
+	/**
+	 * @since 3.4.0
+	 *
+	 * @param $value
+	 */
+	public function update( $value ) {
+		remove_theme_mod( 'background_image_thumb' );
+	}
+}