code: public TableCellStyle findDefaultCellStyle(final int columnIndex) {
          TableCellStyle s = this.defaultCellStyle;
          if (s == null) {
              s = this.parent.findDefaultCellStyle(columnIndex);
          }
          return s;
      }
docs: Find the default cell style for a column
  @param columnIndex the column index
  @return the style, null if none