error

Hi there,
thanks for amazing plugin!

I just got the error could please help me to resolve it?

the header slider has disappeared and it is showing the following message

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘head_code’ not found or invalid function name in /home/…/public_html/wp-includes/plugin.php on line 496

thanks in advance

https://wordpress.org/plugins/header-footer/

https://wordpress.org/plugins/responsive-header-image-slider/