@Override
    public V fetch(final K key,
                   final long time) {
        return getValueOrNull(inner.fetch(key, time));
    }
@Test
    public void shouldReturnPlainKeyValuePairsOnSingleKeyFetch() {
        when(mockedWindowTimestampStore.fetch("key1", 21L))
            .thenReturn(ValueAndTimestamp.make("value1", 42L));
        when(mockedWindowTimestampStore.fetch("unknownKey", 21L))
            .thenReturn(null);

        assertThat(readOnlyWindowStoreFacade.fetch("key1", 21L), is("value1"));
        assertNull(readOnlyWindowStoreFacade.fetch("unknownKey", 21L));
    }