Notice: Undefined index

I give 1 star / 5 stars.

Notice: Undefined index: https in wp-content/plugins/wistia-wordpress-oembed-plugin/wistia-anti-mangler.php on line 572

Line 572: return ‘<script charset=”ISO-8859-1″ src=”http’ . ($_SERVER[‘https’] == ‘on’ ? ‘s’ : ”) . ‘://fast.wistia.com/static/concat/’ . implode($scripts, ‘%2C’) . ‘.js”></script>’;
}

How do I fix this?

Had to change ($_SERVER[‘https’] == ‘on’ to ($_SERVER[‘https’] = ‘on’