Creating a Form to create libraries, import GDS

Hello,

I am trying to write a code to create a form in which I can create a few libraries using a technology (.tf) file and then streamIn the GDS into one for these libraries, but I am stuck at a point where the GDS has to be imported. I still have to add to this code which will instantiate the top cell of the imported GDS into a new Cell view of another library. and then streamout that cellview. Below is the code that I have written so far.

/***************************************************************
*                                                              *
*                       abCreateForm()                         *
*                                                              *
*                     Create the main form                     *
*                                                              *
***************************************************************/
procedure(abCreateForm()
    let((techFile browsetf tfView inpLibName inpGds browseInp sep1 maskLibName maskStrLibName sep2  
        destLibName destCellName destViewName sourceLibName sourceCellName sourceViewName sourceBrowse rotation)
    
    ; techfile browsing and viewing
    
    techFile=hiCreateStringField(
        ?name 'techFile
        ?prompt "Tech File"
       
        )
    
    browsetf=hiCreateButton(
        ?name 'browsetf
        ?buttonText "Browse"
        ?callback "abTechfileBrowseCB()"
        )
    
    tfView=hiCreateButton(
        ?name 'tfView
        ?buttonText "View"
        ?callback "abViewTech()"
        )
    
    ;Input Library and streaming Input GDS
    
    inpLibName=hiCreateStringField(
        ?name 'inpLibName
        ?prompt "Input GDS Library Name"
      
        )
    
    inpGds=hiCreateStringField(
        ?name 'inpGds
        ?prompt "Input GDS to stream"
      
        )
    
    browseInp=hiCreateButton(
        ?name 'browseInp
        ?buttonText "Browse"
        ?callback "abGDSFileBrowseCB()"
        )
    
    sep1=hiCreateSeparatorField(?name 'sep1)
    
    ;Mask Design Library and Mask Structures Library
    
    maskLibName=hiCreateStringField(
        ?name 'maskLibName
        ?prompt "Mask Library Name"
       
        )
    
    maskStrLibName=hiCreateStringField(
        ?name 'maskStrLibName
        ?prompt "Mask Structures Library Name"
        ?callback "abImportGDS()"
        )
    
    sep2=hiCreateSeparatorField(?name 'sep2)
    
    ;Cellview creation and browsing an instance from source library
    
    destLibName=hiCreateStringField(
        ?name 'destLibName
        ?prompt "Enter Library Name"
        ?callback "abCreateInst()"
        )
        
    destCellName=hiCreateStringField(
        ?name 'destCellName
        ?prompt "Enter Cell Name"
        ?callback "abCreateInst()"
        )
        
    destViewName=hiCreateStringField(
        ?name 'destViewName
        ?prompt "Enter View Name"
        ?callback "abCreateInst()"
        )
    
    sourceLibName=hiCreateStringField(
        ?name 'sourceLibName
        ?prompt "Source Library Name"
        ?callback "ddsUpdateSyncWithForm()"
        )
        
    sourceCellName=hiCreateStringField(
        ?name 'sourceCellName
        ?prompt "Source Cell Name"
        ?callback "ddsUpdateSyncWithForm()"
        )
        
    sourceViewName=hiCreateStringField(
        ?name 'sourceViewName
        ?prompt "Source View Name"
        ?callback "ddsUpdateSyncWithForm()"
        )
        
    sourceBrowse=hiCreateButton(
        ?name 'sourceBrowse
        ?buttonText "Browse"
        ?callback "abSyncBrowser()"
        )
        
    rotation=hiCreateRadioField(
        ?name    'rotation
        ?prompt    "Rotation"
        ?choices list("R0" "R90" "R180" "R270" "MY" "MYR90" "MX" "MXR90")
        ?value    "R0"
        ?callback list("abRotationButtonCB()")
        )
        
    hiCreateAppForm(
        ?name 'abInputForm
        ?formTitle "Input Information Form"
        ?fields
            list(
                list(techFile 0:0 450:30 200)
                list(browsetf 450:5 60:25)
                list(tfView 520:5 50:25)
                list(inpLibName 0:30 500:30 200)
                list(inpGds 0:60 500:30 200)
                list(browseInp 500:65 60:25)
                list(sep1 0:95 600:0)
                list(maskLibName 0:100 600:30 200)
                list(maskStrLibName 0:130 600:30 200)
                list(sep2 0:165 600:0)
                list(destLibName 0:170 600:30 200)
                list(destCellName 0:200 600:30 200)
                list(destViewName 0:230 600:30 200)
                list(sourceLibName 0:260 600:30 200)
                list(sourceCellName 0:290 600:30 200)
                list(sourceViewName 0:320 600:30 200)
                list(sourceBrowse 200:350 60:25)
                list(rotation 0:380 600:0 200)
                )
            )
        
        )
    )


/***************************************************************
*                                                              *
*                      abTechfileBrowseCB()                    *
*                                                              *
*                     Browsing the Tech File                   *
*                                                              *
***************************************************************/
procedure(abTechfileBrowseCB()
    ddsFileBrowseCB(
    abInputForm
    'techFile
    "*.tf"
    'browsetf
    )
    )
    
    
/***************************************************************
*                                                              *
*                         abViewTech()                         *
*                                                              *
*                     Viewing the Tech File                    *
*                                                              *
***************************************************************/
procedure(abViewTech()
    view(
    abInputForm->techFile->value
    )
    )
    

/***************************************************************
*                                                              *
*                      abGDSFileBrowseCB()                     *
*                                                              *
*                     Browsing the Input GDS                   *
*                                                              *
***************************************************************/
procedure(abGDSFileBrowseCB()
    ddsFileBrowseCB(
    abInputForm
    'inpGds
    "*.gds"
    'browseInp
    )
    )


/***************************************************************
*                                                              *
*                      abSyncBrowser()                         *
*                                                              *
*                 Synchronise with the browser                 *
*                                                              *
***************************************************************/
procedure(abSyncBrowser()
    ddsSyncWithForm(
    abInputForm
    'sourceBrowse
    'sourceLibName
    'sourceCellNamefileName
    'sourceViewName
    )
    )


/***************************************************************
*                                                              *
*                        abImportGDS()                         *
*                                                              *
*                  Import the GDS into Library                 *
*                                                              *
***************************************************************/
procedure(abImportGDS()
    let((libName libPath techName tfId tfId1 tfId2 GDSName maskLib maskStrLib template)
        libName = abInputForm->inpLibName->value
        libPath = "./"
        techName = abInputForm->techFile->value
        template = "./xstreamInp.temp"
        GDSName = abInputForm->inpGds->value
        maskLib = abInputForm->maskLibName->value
        maskStrLib = abInputForm->maskStrLibName->value
        ddCreateLib(libName libPath)
            tfId = techOpenTechFile(libName techGetDefaultTechName() "w")
            tcLoadTechFile(tfId techName)
            techSaveTechFile(tfId)
            techCloseTechFile(tfId)
            
            xstInSetField("templateFile" template)
            xstInSetField("techFile" techName)
            xstInSetField("library" libName)
            xstInSetField("strmFile" GDSName)
            xstInSetField("logFile" libName.log)
            xstInSetField("summaryFile" libName.sum)
            xstInDoTranslate()
            
            

procedure(xstInOnCompletion(libName)
    printf ("The GDS has been translated")

)

            
        ddCreateLib(maskLib libPath)
            tfId1 = techOpenTechFile(maskLib techGetDefaultTechName() "w")
            tcLoadTechFile(tfId1 techName)
            techSaveTechFile(tfId1)
            techCloseTechFile(tfId1)
            
            
        ddCreateLib(maskStrLib libPath)
            tfId2 = techOpenTechFile(maskStrLib techGetDefaultTechName() "w")
            tcLoadTechFile(tfId2 techName)
            techSaveTechFile(tfId2)
            techCloseTechFile(tfId2)
            
            
            
        )
)









/***************************************************************
*                                                              *
*                        abInput()                             *
*                                                              *
*                       Main entry point                       *
*                                                              *
***************************************************************/

procedure(abInput()
    unless(boundp('abInputForm)
    abCreateForm()
    )
    
    hiDisplayForm(abInputForm)
   
    )

When I load this code and run it in CIW, I get a following message:

INFO (TECH-180006): Compiling class 'controls'....

INFO (TECH-180006): Compiling class 'layerDefinitions'....

*Error* ilGetString: arg must be symbol or string - nil

What am I doing wrong here or what needs to be added/corrected? I am new to SKILL and write few codes after referring to the SKILL guide.