Error in Admin Panel

I tried to activate the TemplatesNext Toolkit plugin in WordPress, but facing an error.
Warning: Cannot assign an empty string to a string offset in C:\xampp\htdocs\practice\wp-customization-practice\free-customization-1\wp-includes\class.wp-scripts.php on line 447

My php version is 7.1

[Note that it works well in php version 5.6]

What should I do?