Absolute Path not detected in Open XML SDK

I am going crazy here. I cannot identify absolute paths in workbooks. The following code returns null on spreadsheets, which I can look in the xml (/xl/workbook.xml) has absolute path.

Can anybody please test the code and confirm if this is a bug ion Open XML SDK or my code?

XML qualified name is "x15ac:absPath".

Link to Open XML SDK info: https://docs.microsoft.com/en-us/dotnet/api/documentformat.openxml.office2013.excelac.absolutepath?view=openxml-2.8.1

Code

using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Spreadsheet;
using DocumentFormat.OpenXml.Office2013.ExcelAc;

public bool Check_AbsolutePath(string filepath)
{
    bool absolutepath = false;

    using (SpreadsheetDocument spreadsheet = SpreadsheetDocument.Open(filepath, false))
    {
        if (spreadsheet.WorkbookPart.Workbook.AbsolutePath != null)
        {
            Console.WriteLine("--> Absolute path to local directory detected");
            absolutepath = true;
        }
    }
    return absolutepath;
}

UPDATE

I have created this as issue on Open XML SDK repo: https://github.com/OfficeDev/Open-XML-SDK/issues/1208