Cannot create new Excel File

[pierreSLA]

Maybe i'm not understanding correctly but if i don't have a template file, how can i create a new excel file.
While updateing the worksheet i get nullreference exception.
Why do i need a template file at all?
var templateFS = File.Create(templateFile) using (FileStream fs = File.Create(tempFile)) using (var fe = new FastExcel.FastExcel(templateFS, fs)) { var ws = new FastExcel.Worksheet(); foreach (var rn in Enumerable.Range(1, 1000)) { var data = new List<Cell>(); var row = new Row(rn, data); data.Add(new Cell(1, $"lala{rn}")); data.Add(new Cell(2, $"{11.1 + rn}")); data.Add(new Cell(3, $"{22.2 + rn}")); ws.AddRow(data); } fe.Update(ws, 0); }