FiX Ensure a null writer doesn't trigger a failure
FiX Ensure a null writer doesn't trigger a failure

A null writer may occur if there's no CDN configured to handle the type
specified for the folder. Ensure it doesn't cause a failure

souldigital/silverstripe-cdncontent,silverstripe-australia/silverstripe-cdncontent,silverstripe-australia/silverstripe-cdncontent,souldigital/silverstripe-cdncontent