OptionalBackgroundBinaryFunction
class OptionalBackgroundBinaryFunction<A, OA : ObservableValue<A>, B, OB : ObservableValue<B>>(argA: OA, argB: OB, lambda: (A, B) -> Background?) : BinaryFunction<Background?, A, OA, B, OB> , ObservableOptionalBackground
Boilerplate which avoids having to use generics.
Similar to BackgroundBinaryFunction, but the value can also be null.