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