public synchronized <U> Versioned<U> map(Function<V, U> transformer) {
        return new Versioned<>(value != null ? transformer.apply(value) : null, version, creationTime);
    }
@Test
    public void testMap() {
        Versioned<String> tempObj = stats1.map(VersionedTest::transform);
        assertThat(tempObj.value(), is("1"));
    }