Runtime Error: expected string got NoneType

[lin-ycv]

Followd the steps in wiki, but got an error

Runtime error (TypeErrorException): expected string, got NoneType

Traceback:
  line 37, in isfile, "C:\Program Files\Rhino 7\Plug-ins\IronPython\Lib\genericpath.py"
  line 147, in checkTheInputs, "<string>"
  line 483, in script

How do I solve this problem?

[Stubbleman]

I replace the line 147
rhinoDocPath = rc.RhinoDoc.ActiveDoc.Path
by
rhinoDocPath = ghenv.Component.OnPingDocument().FilePath
since I usually save .gh only. It works.