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