One can argue that this works as designed - if you mis-click and happen to make a selection where the attribute isn't available, you could potentially get annoyed if the attribute selection got changed on you.

That said, it is likely very confusing, especially for beginners, that it is possible to make impossible selections (combination of a selection of events of some certain event type, with an impossible attribute that isn't available in the event type) resulting in empty flame graphs, even though there are events of the type available.

A less confusing variant would likely be to simply switch to count when the attribute isn't available in the selection.