A funny curiousity - adding `null` as an item is t...

# tornadofx

[edvin]

A funny curiousity - adding null as an item is totally valid for choicebox 🙂

[abhinay]

It is valid for ComboBox as well. It's a regression that swept in 8u20.

https://kotlinlang.slack.com/archives/C136UUPE1/p1543253592434700?thread_ts=1543251824.426200&cid=C136UUPE1