Preconditions:

Some items on sub-items list

Steps:

1. Go to the Content Item preview which has some sub-items
2. Mark several sub-items as checked
3. Click Trash button (or Move)

Actual result:

Error message is shown: An unexpected error occurred while deleting the content item(s). Please try again later.
But after refreshing the page items are removed.
Console shows:

The controller must return a response (Object(EzSystems\EzPlatformAdminUi\REST\Value\BulkOperationResponse) given).

POST http://ezv2/admin/api/ezp/v2/bulk 500 (Internal Server Error)

Expected result:

Sub-items are removed without errors.