Warning: Undefined variable $mysqli in /usr/share/nginx/html/config/sql_session.php on line 16

Fatal error: Uncaught Error: Call to a member function real_connect() on null in /usr/share/nginx/html/config/sql_session.php:16 Stack trace: #0 /usr/share/nginx/html/index.php(2): require_once() #1 {main} thrown in /usr/share/nginx/html/config/sql_session.php on line 16