Parameterize a schematic pcell

I made a schematic pcell for some schematic using technology pcell - the MOS transistors. When I enter a paremeter in the cfd field, the following warning is printed:

*WARNING* (DB-270002): ("times" 0 t nil ("*Error* times: can't handle (\"Wn\" * 1.0)"))

Instead of filling in the value of Wn, that is set in ADE L, the string "Wn" is passed.This causes:
  cdfFormatFloatString( sprintf(nil "%g" (cdfParseFloatString(widN)*factor) ) "n")
to isue a warning.

I understand why, because the type of the cdf parameter widN is string. But how do I make it possible for my pcell to be parametrized, like e.g. transistor pcell provided by the PDK I am using?

Thanks!

Relevant code:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

load("../scripts/CCSinvokeCdfCallbacks.il")
load("../scripts/invChainCCScallbackPatternsToIgnore.il")

let( (library cell pcellID parameters)
library="Playground"
cell="TIC"
unless(ddGetObj(library)
    error("Couldn't open library %L" library)
    )


;-----------------------------------
; Schematic
;-----------------------------------

pcellID=pcDefinePCell(
    list( ddGetObj(library) cell "schematic" "schematic")
    (
        (widN             string        "120n")
    )
    let(    ( cvIDnmos )
      cvIDnmos = dbOpenCellViewByType( libname nchCellName "symbol" nil "r" )
      for( iterator 0 numberOfStages-1
        factor = stageRatio**iterator
        nmos = dbCreateParamInst( pcCellView
            cvIDnmos
            nil    2*iterator+6*ss:0     "R0" 1
            list(
                list("width"    "string"    cdfFormatFloatString( sprintf(nil "%g" (cdfParseFloatString(widN)*factor) ) "n") )
            )
            t
        )  
    )
    CCSinvokeCdfCallbacks(pcCellView ?callInitProc t ?useInstCDF t)
    dbClose(cvIDnmos)
    ); end let

);pcDefinePCell
dbSave(pcellID)
dbClose(pcellID) 

let( (cellID cdfID)
    unless(cellID = ddGetObj( library cell )
        error("Could not get cell %s." cell)
    )
    when(     cdfID = cdfGetBaseCellCDF( cellID )
        cdfDeleteCDF( cdfID )
    )
    cdfID  = cdfCreateBaseCellCDF( cellID )

    cdfCreateParam( cdfID
        ?name            "widN"
        ?type            "string"
        ?defValue        "120n"
        ?units            "lengthMetric"
        ?parseAsNumber    "yes"
        ?prompt        "gate width of first nmos"
        ?display        "t"
    )

);let cdf
);let

 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;