pankajp/traitsui — comment on commit a1072c838681bbaf4eab592bac93ddcffa25b6fc
File: traitsui/editors/tree_editor.py line 113
By rkern:

No way to avoid it, really. It's never bothered me personally because I tend to treat it like `selected` and handle the `None` case as a matter of course. However, it's a fair point. Leaving it as an `Event` is fine.