private @Nullable VirtualFileSystemEntry findChild(VirtualFileSystemEntry parent,
                                                       int childId) {
      if (!(parent instanceof VirtualDirectoryImpl)) {
        return null;
      }
      VirtualFileSystemEntry child = ((VirtualDirectoryImpl)parent).doFindChildById(childId);
      if (child instanceof VirtualDirectoryImpl) {
        if (child.getId() != childId) {
          LOG.error("doFindChildById(" + childId + "): " + child + " doesn't have expected id!");
        }
        VirtualFileSystemEntry old = myIdToDirCache.cacheDirIfAbsent(child);
        if (old != null) child = old;
      }
      return child;
    }
private @Nullable VirtualFileSystemEntry findChild(VirtualFileSystemEntry parent,
                                                       int childId)