@Nullable
  private static Integer getSavedContentId(VirtualFile file) {
    if (!file.isValid()) {
      return null;
    }

    Integer oldContentId = null;
    try(final DataInputStream stream = ACQUIRED_CONTENT_ATTR.readFileAttribute(file)) {
      if (LOG.isDebugEnabled()) {
        LOG.debug("getSavedContentId for " + file + "; stream=" + stream);
      }
      if (stream != null) {
        oldContentId = stream.readInt();
        if (LOG.isDebugEnabled()) {
          LOG.debug("oldContentId=" + oldContentId);
        }
        LOG.assertTrue(oldContentId > 0, oldContentId);
      }
    }
    catch (IOException e) {
      LOG.info(e);
    }
    return oldContentId;
  }
@Nullable
  private static Integer getSavedContentId(VirtualFile file)