code: @Override
      public XlsxWorksheet getSheet(int i)
      {
          XlsxWorksheet ret = null;
          if(sheets != null)
          {
              Sheet sheet = (Sheet)sheets.get(i);
              if(sheet != null)
                  ret = getSheet(sheet.getName());
          }
          return ret;
      }
docs: Returns the worksheet at the given index in the workbook.
  @param i The index of the worksheet
  @return The worksheet at the given index in the workbook