/* Map can be empty if it's an EnumHashBiMap. */
    Map<Currency, String> emptyBimap = EnumHashBiMap.create(Currency.class);
    bimap = EnumHashBiMap.create(emptyBimap);
    assertTrue(bimap.isEmpty());

    /* Map can be empty if it's an EnumBiMap. */
    Map<Currency, Country> emptyBimap2 = EnumBiMap.create(Currency.class, Country.class);
    EnumHashBiMap<Currency, Country> bimap2 = EnumHashBiMap.create(emptyBimap2);

    /* Map can be empty if it's an EnumHashBiMap. */
    Map<Currency, String> emptyBimap = EnumHashBiMap.create(Currency.class);
    bimap = EnumHashBiMap.create(emptyBimap);
    assertTrue(bimap.isEmpty());

    /* Map can be empty if it's an EnumBiMap. */
    Map<Currency, Country> emptyBimap2 = EnumBiMap.create(Currency.class, Country.class);
    EnumHashBiMap<Currency, Country> bimap2 = EnumHashBiMap.create(emptyBimap2);

        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);