@Test
void mapIfPresent() {

    final ToBooleanNullable<String> toBooleanNullable = instance.mapIfPresent(bool -> !bool);
    assertNotNull(toBooleanNullable);
    assertTrue(toBooleanNullable.applyAsBoolean("1"));
    assertFalse(toBooleanNullable.applyAsBoolean("three"));
    assertNull(toBooleanNullable.apply(null));
}