Warning: Undefined variable $mysqli in /customers/e/6/d/virtualized-reality.de/httpd.www/header_categorie.php on line 5

Fatal error: Uncaught Error: Call to a member function query() on null in /customers/e/6/d/virtualized-reality.de/httpd.www/header_categorie.php:5
Stack trace:
#0 /customers/e/6/d/virtualized-reality.de/httpd.www/index.php(2): include()
#1 {main}
  thrown in /customers/e/6/d/virtualized-reality.de/httpd.www/header_categorie.php on line 5