Cannot publish Landing Page with RSS block.

Steps:

1. Create new Landing Page, add name and description.
2. Add RSS block.
3. Add valid xml path.
4. Submit.
5. Publish.

Issue: Error 500, Type error: Argument 2 passed to EzSystems\EzPlatformPageFieldType\FieldType\Page\Storage\DoctrineGateway::insertAttribute() must be of the type string or null, integer given, called in /var/www/temp/vendor/ezsystems/ezplatform-page-fieldtype~/src/lib/FieldType/Page/Storage/PageStorage.php on line 236 [in vendor/ezsystems/ezplatform-page-fieldtype~/src/lib/FieldType/Page/Storage/DoctrineGateway.php:199]