Warning: Undefined variable $conlink in D:\WWWRoot\prottech.com\www\function.php on line 87

Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, null given in D:\WWWRoot\prottech.com\www\function.php:87
Stack trace:
#0 D:\WWWRoot\prottech.com\www\function.php(87): mysqli_query()
#1 D:\WWWRoot\prottech.com\www\product_list.php(6): get_son_tree()
#2 {main}
  thrown in D:\WWWRoot\prottech.com\www\function.php on line 87