IllegalArgumentException.class,
        () -> EnumBiMap.create(Collections.<Currency, Country>emptyMap()));
    assertThrows(
        IllegalArgumentException.class,
        () -> EnumBiMap.create(EnumHashBiMap.<Currency, Country>create(Currency.class)));

    /* Map can be empty if it's an EnumBiMap. */
    Map<Currency, Country> emptyBimap = EnumBiMap.create(Currency.class, Country.class);