XML : Nativescript error when passing response to view

I am trying to send a POST request when an level Of listview(In product.xml) is selected and from the response I am trying to build another listview(In brand.xml).I have succeeded to send the POST request and get the response.But I have failed to pass the response to view.That is I can not build the view.I think the problem is I can't properly send the data(associated with level text),so I failed.I am getting this error:****Attempt to invoke virtual method 'intjave.lang.Integer.intValue()'** on a null object**. null Here is my code-

product.xml:

  <Label text=""  horizontalAlignment="left" verticalAlignment="center" tap="brand" />    

product.Js:

      exports.brand=function (args) {        var item =args.object;         text=item.text;         getBrand(text);         };      function getBrand(data) {        brand.get(data);            frameModule.topmost().navigate("view/brand/brand");    }    

Brand_View_Model:

  function BrandViewModel() {        var viewModel = new Observable({          });        viewModel.get = function (category){          data = category;            }             viewModel.load = function() {               fetch("http://10.0.2.2:8000/user_signup", {             method: "POST",             headers: { "Content-Type": "application/json" },               body: JSON.stringify({                category: data,                })            }).then(function(response) {             return response.json();          }).then(function(data) {                for(var i=0;i<data.length;i++){                viewModel.push({                  brand: data[i].brand,                });               };              });             }        viewModel.empty = function() {      while (viewModel.length) {          viewModel.pop();      }  };        return viewModel;  }    function handleErrors(response) {      if (!response.ok) {          console.log(JSON.stringify(response));          throw Error(response.statusText);      }      return response;  }     module.exports = BrandViewModel;    

** Brand.js:**

  var BrandViewModel = require("../../shared/brand_view_model");    var observableModule = require("data/observable");    var page;    var data;    var brandList = new BrandViewModel([]);        var pageData = new observableModule.fromObject({      brandList: brandList  });      exports.loaded = function(args) {      page = args.object;        page.bindingContext = pageData;        brandList.empty();      brandList.load();      };    

Brand.xml:

  <Page loaded="loaded">      <GridLayout>          <ListView items="" >              <ListView.itemTemplate>                  <Label text=""  horizontalAlignment="left" verticalAlignment="center" tap="brand" />              </ListView.itemTemplate>          </ListView>        </GridLayout>  </Page>