@Nullable
  public String readCurrentRevision() {
    if (!isDirStateInfoAvailable()) return null;
    try {
      return BaseEncoding.base16().lowerCase().encode(readHashBytesFromFile(myDirStateFile));
    }
    catch (IOException e) {
      // dirState exists if not fresh,  if we could not load dirState info repository must be corrupted
      LOG.error("IOException while trying to read current repository state information.", e);
      return null;
    }
  }
@Nullable
  public String readCurrentRevision()