It is possible to handle how (and if) null should be handled in your picklist / combobox / dropdown with the Null / NullRep options for the picklist in the ViewModel editor.
It works like this:
- None - no null option in the picklist
- First - null should be available to choose, and should be first
- Last - null should be available to choose, and should be last
- IfEmpty - null should be shown when nothing is yet selected, but not possible to choose once the user has selected any other option
The text in the NullRep textbox defines the text to display for the null option. For example "Choose a color".