Error 500 on preview when creating new folder.

Steps:
1. Log into studio demo.
2. Go to Content / Content structure.
3. Click Create and choose Folder.
4. Fill all fields.
5. Check the preview.
Actual: Error 500.
Expected: Preview is generated w/o errors.

Remarks: Exception from log attached. Verified that it does not occur on pure platform. Also does not occur on studio clean.
(occurs with and without yoochoose integration)