ID 250770 - LookupCurves Knob created via Python can't be saved.

Problem summary
When a Lookup curve is used for making custom gizmos,  a " Obsolete_knob curve call is wrong, probably a missing NULL for script argument" error is generated.

Customer reported version
nuke.9.0v8

Customer reported platform
fedora

Steps to reproduce

1 - Create a NoOp node.
2 - Select it and run the following code:
nuke.selectedNode().addKnob(nuke.LookupCurves_Knob('', 'curve'))
The lookup curve is added, with a default curve.
3 - Save script or Copy NoOp node
4 - Open Script or Paste Node
5 - Error: Obsolete_knob curve call is wrong, probably a missing NULL for script argument

Workaround
Unknown. 

Reproduced by support
Reproduced by support. Nuke 10.5v1 (Windows7)

Expected behaviour
Be able to create Lookup curve knobs using 'addKnob' calls. 

Actual behaviour
Lookup curve knobs cannot be created using `addKnob` calls.