title: Puzzle: what's wrong with this snippet
body: <p>... and how did it happen (guessing allowed, of course :-)</p>
  
  <pre><code>@Override
  public int convertChildIndexToModel(int modelIndex) {
      return getRowSorter() != null ? getRowSorter()
              .convertRowIndexToView(modelIndex) : modelIndex;
  }
  
  @Override
  public int convertChildIndexToView(int viewIndex) {
      return getRowSorter() != null ? getRowSorter()
              .convertRowIndexToModel(viewIndex) : viewIndex;
  }
  </code></pre>
  
  <p>and yeah, the idiot was me ;-)</p>