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