Lunchbox “Curves.ShortestWalk” does not work

Hey, I’m trying to use shortest walk within a curve network, but i got this message : Warning: Curves.ShortestWalk operation failed.
Method not found: 'Autodesk.DesignScript.Geometry.PolyCurve Autodesk.DesignScript.Geometry.PolyCurve.ByJoinedCurves

can anybody help me to resolve this