If it doesn't, then our roles start filling up the other Qt ones such as
AccessibleDescription. Instead we need to start UserRole (except for
DisplayRole of course.)
Normally if a malformed event is empty it will just be empty space - but
that looks buggy. Instead, we can add a message saying "This event does
not have any content."
BUG: 494093
Most of the data in the objects will be empty, but at least a valid matrix id is provided.
This fixes missing data in some places in the UI (e.g., in HiddenDelegate)
