private static Couple<DirDiffElementImpl> getSelectedSourceAndTarget(DirDiffTableModel model) {
    List<DirDiffElementImpl> elements = model.getSelectedElements();
    if (elements.size() != 2) return null;
    DirDiffElementImpl source = ContainerUtil.find(elements, DirDiffElementImpl::isSource);
    DirDiffElementImpl target = ContainerUtil.find(elements, DirDiffElementImpl::isTarget);
    if (source == null || target == null || source.getParentNode() != target.getParentNode()) return null;
    return Couple.of(source, target);
  }
private static Couple<DirDiffElementImpl> getSelectedSourceAndTarget(DirDiffTableModel model)