Edited Unassigned: Setting null or blank formula on a multi-cell range causes broken shared formula [15056]

Using 3.1 Stable (https://epplus.codeplex.com/SourceControl/changeset/d09aa5eaced9) :

var path = @"C:\path\to\output.xlsx";
var file = new FileInfo(path);
file.Delete();
using (var ep = new ExcelPackage(file))
{
var s = ep.Workbook.Worksheets.Add("test");
s.Cells["A1:A2"].Formula = ""; // or null, or non-empty whitespace, with same result
ep.Save();
}

Open the generated XLSX file. Excel detects a problem with the shared formula and repairs/removes it. For example, see attached capture.

Also occurs in:

* 4.0 Beta 2 (https://epplus.codeplex.com/SourceControl/changeset/aec70b7f9b2e)
* Latest 4.0.0.1 as of OP (https://epplus.codeplex.com/SourceControl/changeset/f229eb1e3c82)

Does not occur when setting a non-null non-blank formula.