Optional port for Node Geometry Editor Frame?

How do you create an optional port for a frame? I want to have rotation port which defaults to 0 if not attached:

you do not wire it and then you select the port itself and flag it as visible in frame

I tried that

and got this error:
10:35:5: Build of NodeGeometry failed: input input from block To radians[GeometryTrigonometryBlock] is not connected and is not optional.

Yeah because that node needs a type
But you can add a converter before.