I believe if value set to default NUIConverter will return UIKeyboardAppearanceDefault, because none if/else branches will be triggered (I modeled behavior after toControlContentVerticalAlignment). Or you are suggesting to raise exception?

Ah I see. That works.

I was thinking of having all values having to be explicitly specified, and if it was misspelt or an invalid value (i.e. blue) it should merely not set that property's value and move on (don't even return a default, just avoid setting the property and move on). But considering this is a common pattern found throughout the codebase I think it fine for now. Although, I would like to change it sometime in the future.

Good job on conforming to coding conventions in this project, by the way.

LGTM