Curve Mapper loses its curve when performing specific actions

Created by: mnn

Problem statement

When duplicating a curve mapper or creating a monad with a curve mapper, only a blank curve mapper node is created, the curve is lost.

Steps to reproduce

1. Create Curve Mapper node with custom curve
2. Duplicate the node

Expected result

The curve is duplicated along with other node data.

Actual result

Curve Mapper without curve (actually even the default curve is not shown, you have change some other value in the node to get it to show, so you can edit it).

Sverchok version

0.6.0.0

I believe it's the "stable Oktober 2020" v2, installed from inside Blender (Add-ons -> Install...)