@Override
  public String toUrlValue() {
    if (this == UNKNOWN) {
      throw new UnsupportedOperationException("Shouldn't use TravelMode.UNKNOWN in a request.");
    }
    return name().toLowerCase(Locale.ENGLISH);
  }
Indicates an unknown travel mode returned by the server. The Java Client for Google Maps
Services should be updated to support the new value.
src/main/java/com/google/maps/model/TravelMode.java