- Add Dynamic Data Lists portlet to new page.
- Create new list with definition (e.g. To Do list)
- Go to Configuration to enable Spreadsheet View.
- Double click on an Attachment cell, click choose.
- Add a basic document in root folder.
- Go to Admin > Site Administration: Content > Documents and Media
- Move the root document to the recycle bin
- Navigate to the DDL and try to remove the attachment that is no longer there
There is no way for users to clear the contents of the attachment cell, even if the attachment is no longer available.