code: public Cell<C, T> row() {
          if (cells.size() > 0)
              endRow();
          if (rowDefaults != null)
              toolkit.freeCell(rowDefaults);
          rowDefaults = toolkit.obtainCell(this);
          rowDefaults.clear();
          return rowDefaults;
      }
docs: Indicates that subsequent cells should be added to a new row and returns
  the cell values that will be used as the defaults for all cells in the
  new row.