addNonNull(h);
addNonNull(h, JScrollPane.COLUMN_HEADER);
  public void setColumnHeader(JViewport h)  {    if (columnHeader == h)      return;        JViewport old = columnHeader;    removeNonNull(old);    columnHeader = h;    addNonNull(h);    firePropertyChange("columnHeader", old, h);    sync();  }