How to declare return type Future<int?>

[Zverik]

I could not find any example of a nullable type in a generic. Not a single List<String?> or Future<File?>.

For a regular Future<int> we use BridgeTypeAnnotation(BridgeTypeRef(CoreTypes.future, [CoreTypes.int])). For Future<int>? we could add , nullable: true to the annotation. But what to do when the generic type itself is optional?