code: public static Optional<Guid> getWorkUnitGuid(State state)
        throws IOException {
      if (state.contains(WORK_UNIT_GUID)) {
        return Optional.of(Guid.deserialize(state.getProp(WORK_UNIT_GUID)));
      }
      return Optional.absent();
    }
docs: Get guid in this state if available. This is the reverse operation of {@link #setWorkUnitGuid}.
  @param state State from which guid should be extracted.
  @return A byte array guid.
  @throws IOException