ERROR: Using null as an array offset is deprecated, use an empty string instead
FILE: /var/www/html/wp-includes/functions.php:1189

#0 /var/www/html/wp-includes/functions.php(1189): {closure:/var/www/html/wp-config.php:22}()
#1 /var/www/html/wp-content/plugins/wp-optimize/minify/class-wp-optimize-minify-front-end.php(812): add_query_arg()
#2 /var/www/html/wp-includes/class-wp-hook.php(341): WP_Optimize_Minify_Front_End->process_header_css()
#3 /var/www/html/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters()
#4 /var/www/html/wp-includes/plugin.php(522): WP_Hook->do_action()
#5 /var/www/html/wp-includes/functions.wp-styles.php(57): do_action()
#6 /var/www/html/wp-includes/class-wp-hook.php(341): wp_print_styles()
#7 /var/www/html/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters()
#8 /var/www/html/wp-includes/plugin.php(522): WP_Hook->do_action()
#9 /var/www/html/wp-includes/general-template.php(3197): do_action()
#10 /var/www/html/wp-includes/template-canvas.php(17): wp_head()
#11 /var/www/html/wp-includes/template-loader.php(132): include('...')
#12 /var/www/html/wp-blog-header.php(19): require_once('...')
#13 /var/www/html/index.php(17): require('...')