Fatal error: Uncaught Error: Class 'WP_Customize_Panel' not found in /home/qrmil/public_html/wp-includes/customize/class-wp-customize-themes-panel.php:17
Stack trace:
#0 {main}
thrown in /home/qrmil/public_html/wp-includes/customize/class-wp-customize-themes-panel.php on line 17