public static String GetCellData(this ISheet sheet, Int32 x, Int32 y)
        {
            String value = null;
            var    cell  = OfficeAssistor.GetCell(sheet, x, y);

            if (cell != null)
            {
                value = cell.ToString();
            }
            return(value);
        }
        public static Double?GetCellDataDouble(this ISheet sheet, Int32 x, Int32 y)
        {
            Double?value = null;
            ICell  cell  = OfficeAssistor.GetCell(sheet, x, y);

            if (cell != null)
            {
                if (cell.CellType == CellType.String)
                {
                    String valueStr = cell.ToString();
                    if (Double.TryParse(valueStr, out Double doubleValue))
                    {
                        value = doubleValue;
                    }
                }
                else
                {
                    value = cell.NumericCellValue;
                }
            }

            return(value);
        }