class ApiCalls {
val client = OkHttpClient()
val list: ArrayList<VehicleListModel>? = null
public fun getEnquiryList(id:String): ArrayList<EnquiryModel>? {
    return null
}
public fun getVehicleList(): ArrayList<VehicleListModel> {


    val body = FormBody.Builder()
            .build()
    val request = Request.Builder()
            .post(body)
            .url(URLs.URL_GET_VEHICLE_LIST)
            .build()
    val callGetVehicleList = client.newCall(request)
    callGetVehicleList?.enqueue(object : Callback {
        override fun onFailure(call: Call?, e: IOException?) {
            if (call == null || call.isCanceled)
                return

        }

        override fun onResponse(call: Call?, response: Response?) {
            if (call == null || call.isCanceled)
                return
            val resp = response?.body()?.string()

            try {


                val jo = JSONObject(resp)
                val message = jo.getJSONArray("VehicleModelList")

                for (i in 0 until message.length()) {
                    val json = message.getJSONObject(i)
                    val vehicleListId = json.getString("_id")
                    val vehicleListName = json.getString("vehicle_model_name")
                    val vehicle = VehicleListModel(vehicleListId, vehicleListName)
                    if (list != null) {
                        list.add(vehicle)
                    }
Log.e("....................",vehicleListId)
                }

            } catch (e: Exception) {


            }
        }

    })


    return list!!
}

list= ApiCalls().getVehicleList()
    for (i in 0 until list.size)
    {
        labels.add(list[i].vehicleName)
    }
    val adapter = ArrayAdapter(context, android.R.layout.simple_spinner_item, labels)

    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)

    vehiclelist.adapter = adapter

FATAL EXCEPTION: main
Process: abc.com.app, PID: 23077
kotlin.KotlinNullPointerException