pfSense

How to reproduce:
Unselect all interfaces on the services_dhcpv6_relay.php and uncheck "Enable"
Result:

Crash report details:

PHP Errors:
[27-May-2021 18:11:36 Europe/Moscow] PHP Warning:  implode(): 
Invalid arguments passed in /usr/local/www/services_dhcpv6_relay.php on line 130

It should check `interface` array, see https://github.com/pfsense/pfsense/blob/cf8a0761c5c2ae80b62743d6d476e0fae6f2495e/src/usr/local/www/services_dhcp_relay.php#L115:

        if (isset($_POST['interface']) &&
            is_array($_POST['interface'])) {
            $config['dhcrelay']['interface'] = implode(",",
                $_POST['interface']);
        }