google apps script - Typo error: Cannot call method "getDataRange" of null -

im trying publish code, everytime when run code error cannot call method"getdatarange" of null. please me sort out .here code function

doget() {    var ss = spreadsheetapp.openbyid('sheet id'); var sheet = ss.getsheetbyname('sheet name'); var data = sheet.getdatarange();  var datefilter= charts.newcategoryfilter().setfiltercolumnindex(0).build();  var agefilter = charts.newnumberrangefilter().setfiltercolumnindex(7).build(); var transportfilter = charts.newcategoryfilter().setfiltercolumnindex(2).build(); var namefilter = charts.newstringfilter().setfiltercolumnindex(1).build();  var tablechart = charts.newtablechart().setdimensions(700, 300)                  .setdataviewdefinition(charts.newdataviewdefinition().setcolumns([0,1,2,3,4,5,6,7]))                 .build();  var piechart = charts.newpiechart()               .setdataviewdefinition(charts.newdataviewdefinition()               .setcolumns([1,7])).build();  var dashboard = charts.newdashboardpanel().setdatatable(data)              .bind([datefilter,agefilter, transportfilter, namefilter], [tablechart,    piechart])              .build();  var app = uiapp.createapplication().setheight(50);  var todaysdate = new date(); app.add(app.createlabel(todaysdate)); app.add(app.createhtml('<h1 style="text-align:center;">demo</h1>'));  var filterpanel = app.createhorizontalpanel(); var chartpanel = app.createhorizontalpanel();   filterpanel.add(datefilter).add(agefilter).add(transportfilter).add(namefilter).setspacing(10); chartpanel.add(tablechart).add(piechart).setspacing(50);  dashboard.add(app.createverticalpanel().add(filterpanel).add(chartpanel)); app.add(dashboard);  var service = scriptapp.getservice(); service.enable(service.restriction.all);  return app; } 

the error indicate sheet null. make sure using correct sheet name in var sheet = ss.getsheetbyname('sheet name');. copy , paste sheet name google doc if there invisible characters.