phpMyFAQ Fatal error

Uncaught exception: 'TypeError'

Message: 'phpMyFAQ\Strings::htmlentities(): Argument #1 ($string) must be of type string, null given, called in /var/www/html/faq/add.php on line 70'

Stack trace:

#0 /var/www/html/faq/add.php(70): phpMyFAQ\Strings::htmlentities()
#1 /var/www/html/faq/index.php(793): require('...')
#2 {main}

Thrown in '/var/www/html/faq/src/phpMyFAQ/Strings.php' on line 274