Error with no plugins installed

[Adrian-S]

First of all I was not the one to purchase the theme so I can't contact you via support.

Sooo... With "Javascript file merging and compression" enabled I get this error, and it's gone if it's disabled. This is on v4.9.2.3.

But I think I have the reason in my case. Site had no plugin installed, so I installed and activated Error Log Monitor and the site fixed it's self. Error was back with plugin disabled. Later on I installed Wordfence thinking it was hacked or something, but no problems were found. But I notice site was working Error Log Monitor disabled.

The only logical conclusion was that if the site had no plugin enabled the error would occur.

The error:

Fatal error: Uncaught Error: Attempt to assign property "extra" on null in /wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/class-asset-manager.php:913
Stack trace: 
#0 /wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/class-asset-manager.php(289): aviaAssetManager->try_deregister_scripts('avia-head-scrip...') 
#1 /wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/class-asset-manager.php(104): aviaAssetManager->merge('js', 'avia-head-scrip...', Array) 
#2 /wp-includes/class-wp-hook.php(308): aviaAssetManager->try_minifying_scripts('') 
#3 /wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters(NULL, Array) 
#4 /wp-includes/plugin.php(517): WP_Hook->do_action(Array) 
#5 /wp-includes/script-loader.php(2194): do_action('wp_enqueue_scri...') 
#6 /wp-includes/class-wp-hook.php(308): wp_enqueue_scripts('') 
#7 /wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters(NULL, Array) 
#8 /wp-includes/plugin.php(517): WP_Hook->do_action(Array) 
#9 /wp-includes/general-template.php(3049): do_action('wp_head') 
#10 /wp-content/themes/enfold/header.php(195): wp_head() 
#11 /wp-includes/template.php(783): require_once('/var/www/1/6521...') 
#12 /wp-includes/template.php(718): load_template('/var/www/1/6521...', true, Array) 
#13 /wp-includes/general-template.php(48): locate_template(Array, true, true, Array) 
#14 /wp-content/themes/enfold/template-builder.php(15): get_header() 
#15 /wp-includes/template-loader.php(106): include('/var/www/1/6521...') 
#16 /wp-blog-header.php(19): require_once('/var/www/1/6521...') 
#17 /index.php(17): require('/var/www/1/6521...') 
#18 {main} thrown in /wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/class-asset-manager.php on line 913

Hope this info helps somebody. I will leave "Wordfence" enabled anyway, so my problem is gone.