Null Reference Exception when saving list of numbers.

[Brady Kelly]

If I run the following code, my workbook gets saved nicely, with a short list of year numbers:

` {
using (ExcelPackage pck = new ExcelPackage(new FileInfo(TheFile)))
{
var listSheet = pck.Workbook.Worksheets.Add("LISTS");

        listSheet.Cells["E1"].Value = "Heading";
        for (var i = 2; i < 10; i++)
        {
            listSheet.Cells[$"E{i}"].Value = (DateTime.Now.Year - i);
        }
        pck.Save();
    }
}`

If I remove the code listSheet.Cells["E1"].Value = "Heading";, then pck.Save(); fails with a Null Reference Exception. EPPlus doesn't like columns of numbers without a header.