code: public Cell<C, T> getCell(C widget) {
          for (int i = 0, n = cells.size(); i < n; i++) {
              Cell<C, T> c = cells.get(i);
              if (c.widget == widget)
                  return c;
          }
          return null;
      }
docs: Returns the cell for the specified widget in this table, or null.