Fatal error: Uncaught TypeError: mysqli_real_escape_string(): Argument #1 ($mysql) must be of type mysqli, null given in /var/www/html/header.php:20 Stack trace: #0 /var/www/html/header.php(20): mysqli_real_escape_string(NULL, '/') #1 /var/www/html/index.php(2): require('/var/www/html/h...') #2 {main} thrown in /var/www/html/header.php on line 20