modify PCell parameter due to skill code

Hi all,

I want to modify some parameters of PCell due to skill code. the code is in the following:

procedure(modifyCDFParam()

   let((cv cvSch cdfData)

   cv=geGetEditCellView()

  cvSch=dbOpenCellViewByType(cv~>libName cv~>cellName "schematic" "schematic")

  foreach(inst cvSch~>instances

   cdf=cdfGetInstCDF(inst)

   vfoSetParam(cdfData "sdMtlWidth" "280n")

  vfoSetParam(cdfData "leftTap" nil)

             )

       )
                )

when I load the code and run the the function modifyCDFParam(), the code don't work and show the error: *Error* putprop: first arg must be either symbol, list, defstruct or user type - nil.

does anyone help to debug what is the problem of the code?

thanks