UnwrapElement won't work for Dynamo Plane


I’m tried to create sketch plane with python script in Dyanamo.
I’ve read this article

and tried, (below is only part of code)

rPln = UnwrapElement(IN[0])

# Set the reference plane as the sketchplane in the active view in another transaction
sp = SketchPlane.Create(doc,rPln)
doc.ActiveView.SketchPlane = sp

by IN[0] a Plane is given, that is created through Dynamo Plane.ByTreePoints.
However, Python Node give me Type error message,

“Warning: IronPythonEvaluator.EvaluateIronPythonScript operation failed. Traceback (most recent call last): File “”, line 41, in TypeError: expected Plane, got Plan”

Can somebody tell me, what did I wrong?