kotlin.kotlinnullpointerexception - json

Question

JSON displays data get in Android and shows in TextView and TableLayout.JSON have Nine Records and its parsing using Retrofit2 and RXjava2.
All the data gets in android side and Store in ArrayList.
In ArrayList Size is Nine get All Data.
Textview shows data but in TableLayout only two record display another seven record is not display. in Third record goeson var tax_total its give Error : "kotlin.kotlinnullpointerexception"
What's the problem that the other data is not displayed?
private fun fetchYearData(){
val retrofit = APIClient.apIClient
if (retrofit != null) {
api = retrofit.create(APIInterface::class.java)
}
compositeDisposable!!.add(api.getSalesGSTData(1,1,"04/01/2018","31/03/2019")
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe( {
displaySalesGSTData(it.salesGst) },
{
Toast.makeText(this,it.message,Toast.LENGTH_LONG).show() }))
}
private fun displaySalesGSTData(salesGSt : List<SalesGST>) {
salesGST = SalesGST()
tvSalesCompanyName.setText(salesGSt.get(1).Cmp_Name)
tvGSTIN.setText(salesGSt.get(1).GSTIN)
val rowHeader = TableRow(this#Sales)
rowHeader.setBackgroundColor(Color.parseColor("#c0c0c0"))
rowHeader.setLayoutParams(TableLayout.LayoutParams(TableLayout.LayoutParams.MATCH_PARENT,
TableLayout.LayoutParams.WRAP_CONTENT))
val headerText = arrayOf<String>("Sr.No.", "Invoice Type", "Bill No.", "Bill Date", "Firm Name", "GST NO","TAX Total","CGST","SGST","IGST","Net Amount")
for (c in headerText)
{
val tv = TextView(this#Sales)
tv.setLayoutParams(TableRow.LayoutParams(TableRow.LayoutParams.WRAP_CONTENT,
TableRow.LayoutParams.WRAP_CONTENT))
tv.setGravity(Gravity.CENTER)
// tv.setBackgroundResource(R.drawable.table_header)
tv.setTextColor(Color.parseColor("#3F51B5"))
tv.setTextSize(18F)
tv.setPadding(5, 5, 5, 5)
tv.setText(c)
rowHeader.addView(tv)
}
tableMarks.addView(rowHeader)
for (j in 0 until salesGSt.size)
{
var fName : String = salesGSt[j].FirmName!!
var invoice : String = salesGSt[j].InvoiceType!!
var bill_no : String = salesGSt[j].ChallanNo!!
var bill_date : String = salesGSt[j].ChallanDate!!
var gst_no : String = salesGSt[j].PartyGST!!
var tax_total : String = salesGSt[j].TaxTotal!!
var cgst : String = salesGSt[j].CGSTTotal!!
var igst : String = salesGSt[j].IGSTTotal!!
var sgst : String = salesGSt[j].SGSTTotal!!
var net_amount : String = salesGSt[j].ChallanAmount!!
var sr : Int = j
// dara rows
val row = TableRow(this#Sales)
row.setLayoutParams(TableLayout.LayoutParams(TableLayout.LayoutParams.MATCH_PARENT,
TableLayout.LayoutParams.WRAP_CONTENT))
val colText = arrayOf<String>(sr.toString(),(invoice), bill_no, bill_date, fName, gst_no,tax_total,cgst,sgst,igst,net_amount)
for (text in colText)
{
val tv = TextView(this#Sales)
tv.setLayoutParams(TableRow.LayoutParams(TableRow.LayoutParams.WRAP_CONTENT,
TableRow.LayoutParams.WRAP_CONTENT))
tv.setGravity(Gravity.CENTER)
// tv.setBackgroundResource(R.drawable.table_shape)
tv.setTextSize(18F)
tv.setTextColor(Color.parseColor("#000000"))
tv.setPadding(5, 5, 5, 5)
tv.setText(text)
row.addView(tv)
}
tableMarks.addView(row)
}
JSON :
{"success":1,"salesGst":[{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"SALES GJ","ChallanNo":"1","ChallanDate":"2019-03-15 00:00:00","ChallanAmount":"2778.75","TaxTotal":"2778.75","InvoiceType":"Retail Invoice","CGSTTotal":"0.0","PartyGST":"CDE","SGSTTotal":"0.0","IGSTTotal":"0.0"},{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"SALES GJ","ChallanNo":"1","ChallanDate":"2019-03-13 00:00:00","ChallanAmount":"2203.0","TaxTotal":"2118.5","InvoiceType":"Tax Invoice","CGSTTotal":"52.96","PartyGST":"CDE","SGSTTotal":"52.96","IGSTTotal":"0.0"},{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"VIKAS","ChallanNo":"2","ChallanDate":"2019-03-16 00:00:00","ChallanAmount":"6975.0","TaxTotal":"6975.0","InvoiceType":"Retail Invoice","CGSTTotal":"0.0","PartyGST":null,"SGSTTotal":"0.0","IGSTTotal":"0.0"},{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"SALES MH","ChallanNo":"2","ChallanDate":"2019-03-13 00:00:00","ChallanAmount":"420.0","TaxTotal":"403.75","InvoiceType":"Tax Invoice","CGSTTotal":"0.0","PartyGST":"ABC","SGSTTotal":"0.0","IGSTTotal":"20.19"},{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"SALES GJ","ChallanNo":"3","ChallanDate":"2019-03-14 00:00:00","ChallanAmount":"4788.0","TaxTotal":"4560.0","InvoiceType":"Tax Invoice","CGSTTotal":"114.0","PartyGST":"CDE","SGSTTotal":"114.0","IGSTTotal":"0.0"},{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"SALES GJ","ChallanNo":"4","ChallanDate":"2019-03-15 00:00:00","ChallanAmount":"241.9","TaxTotal":"230.38","InvoiceType":"Tax Invoice","CGSTTotal":"5.76","PartyGST":"CDE","SGSTTotal":"5.76","IGSTTotal":"0.0"},{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"SALES GJ","ChallanNo":"5","ChallanDate":"2019-03-15 00:00:00","ChallanAmount":"5563.68","TaxTotal":"5101.5","InvoiceType":"Tax Invoice","CGSTTotal":"231.28","PartyGST":"CDE","SGSTTotal":"231.28","IGSTTotal":"0.0"},{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"SALES GJ","ChallanNo":"6","ChallanDate":"2019-03-16 00:00:00","ChallanAmount":"13238.0","TaxTotal":"12459.25","InvoiceType":"Tax Invoice","CGSTTotal":"389.29","PartyGST":"CDE","SGSTTotal":"389.29","IGSTTotal":"0.0"},{"Cmp_Name":"ABC","GSTIN":"AAAA","FirmName":"SALES MH","ChallanNo":"7","ChallanDate":"2019-03-16 00:00:00","ChallanAmount":"2074.0","TaxTotal":"1975.0","InvoiceType":"Tax Invoice","CGSTTotal":"0.0","PartyGST":"ABC","SGSTTotal":"0.0","IGSTTotal":"98.75"}]}
xml :
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">
<HorizontalScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true"
android:scrollbarStyle="insideInset"
android:fadeScrollbars="true"
android:scrollbarSize="10dp"
android:fitsSystemWindows="true">
<TableLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/tableMarks"
android:stretchColumns="*"
android:layout_marginTop="20dp"
android:orientation="horizontal"
></TableLayout>
</HorizontalScrollView>
</ScrollView>