@Test
void testMap() {

    final Optional<String> binLen = instance.map(String::length).map(Integer::toBinaryString).findFirst();
    assertEquals(Optional.of("1"), binLen);
    Optional<String> r = SingletonStream.of("C").map(s -> null).map(a -> "Olle").findAny();
    assertEquals(Optional.of("Olle"), r);
}