private @Nullable VirtualFile findRoot(Library library) {
      for (VirtualFile classesRoot : library.getFiles(OrderRootType.CLASSES)) {
        if (VfsUtilCore.isAncestor(classesRoot, myClassFile, true)) {
          return classesRoot;
        }
      }
      return null;
    }
private @Nullable VirtualFile findRoot(Library library)