public string GetNumberFormatString(int i)
{
if (RowCells == null)
{
throw new InvalidOperationException("No data exists for the row/column.");
}
if (RowCells[i] == null)
{
return(null);
}
if (RowCells[i].EffectiveStyle == null)
{
return(null);
}
return(Workbook.GetNumberFormatString(RowCells[i].EffectiveStyle.NumberFormatIndex)?.FormatString);
}