Error Input string was not in a correct format. C#

Question

follows below my code `if (actualValue != "") { capacityimportData = new Capacityimport();

                capacityimportData.Quantity = Convert.ToInt16(actualValue);
                var data = "";
                if (sheet.GetRow(2).GetCell(actualColumn).CellType == CellType.String)
                {
                    data = sheet.GetRow(2).GetCell(actualColumn).StringCellValue;

                }
                else if (sheet.GetRow(2).GetCell(actualColumn).CellType == CellType.Numeric)
                {          

                    data = sheet.GetRow(2).GetCell(actualColumn).NumericCellValue.ToString();
                   
                }`