Internal Server Error when clicking on Payment Preferences

[jz2]

Hi,

when clicking on Payment Preferences in the back-office I get an Internal Server Error. I enabled the debug mode to get a clearer error message by editing `config / defines.inc.php` like so:

```php

if (!defined('_PS_MODE_DEV_')) {
    define('_PS_MODE_DEV_', true);
}

```

As soon as it was set to `true`, the error disappeared. After setting the debug mode back to `false` the error appeared again.

Prestashop 1.7.6.5 on PHP 7.2

Thanks for your help.