@Nullable
  private Node[] getSelectedNodes() {
    TreePath[] leadSelectionPath = myTree.getSelectionPaths();
    if (leadSelectionPath == null || leadSelectionPath.length == 0) return null;

    final List<Node> result = new ArrayList<Node>();
    for (TreePath comp : leadSelectionPath) {
      final Object lastPathComponent = comp.getLastPathComponent();
      if (lastPathComponent instanceof Node) {
        final Node node = (Node) lastPathComponent;
        result.add(node);
      }
    }
    return result.isEmpty() ? null : result.toArray(new Node[result.size()]);
  }
  @Override
  @Nullable
  public Set<Usage> getSelectedUsages() {
    TreePath[] selectionPaths = myTree.getSelectionPaths();
    if (selectionPaths == null) {
      return null;
    }

    Set<Usage> usages = new THashSet<Usage>();
    for (TreePath selectionPath : selectionPaths) {
      DefaultMutableTreeNode node = (DefaultMutableTreeNode) selectionPath.getLastPathComponent();
      collectUsages(node, usages);
    }

    return usages;
  }
  @Nullable
  private UsageTarget[] getSelectedUsageTargets() {
    TreePath[] selectionPaths = myTree.getSelectionPaths();
    if (selectionPaths == null) return null;

    Set<UsageTarget> targets = new THashSet<UsageTarget>();
    for (TreePath selectionPath : selectionPaths) {
      Object lastPathComponent = selectionPath.getLastPathComponent();
      if (lastPathComponent instanceof UsageTargetNode) {
        UsageTargetNode usageTargetNode = (UsageTargetNode) lastPathComponent;
        UsageTarget target = usageTargetNode.getTarget();
        if (target != null && target.isValid()) {
          targets.add(target);
        }
      }
    }

    return targets.isEmpty() ? null : targets.toArray(new UsageTarget[targets.size()]);
  }