ChoiceBox keeps selected item when the underlying collection is replaced.

To reproduce:
1. Click 'Set data' button.
2. Select any item.
3. Push 'Show selected item' button. It will print out selected item value.
4. Push 'Set empty list' button.
=>Push 'Show selected item' button. It will print out previous selected item value.
Expected behavior is to recieve 'null'.