code: @Override
    public XSSFRichTextString getRichStringCellValue() {
      CellType cellType = getCellType();
      XSSFRichTextString rt;
      switch (cellType) {
        case BLANK:
          rt = new XSSFRichTextString("");
          break;
        case STRING:
          rt = new XSSFRichTextString(getStringCellValue());
          break;
        default:
          throw new NotSupportedException();
      }
      return rt;
    }
docs: Get the value of the cell as a XSSFRichTextString
  <p>
  For numeric cells we throw an exception. For blank cells we return an empty string.
  For formula cells we return the pre-calculated value if a string, otherwise an exception
  </p>
  @return the value of the cell as a XSSFRichTextString