private static Set<PsiFile> getSelectedScope(final Tree tree) {
    TreePath[] paths = tree.getSelectionPaths();
    if (paths == null || paths.length != 1) return EMPTY_FILE_SET;
    PackageDependenciesNode node = (PackageDependenciesNode)paths[0].getLastPathComponent();
    if (node.isRoot()) return EMPTY_FILE_SET;
    Set<PsiFile> result = new HashSet<>();
    node.fillFiles(result, true);
    return result;
  }
private static Set<PsiFile> getSelectedScope(final Tree tree)