public static <K, V> Entry<K, V> entry(@Nullable K key, @Nullable V value) {
        return new SimpleImmutableEntry<>(key, value);
    }
@Test
    public void when_entry() {
        Entry<String, Integer> e = entry("key", 1);
        assertEquals("key", e.getKey());
        assertEquals(Integer.valueOf(1), e.getValue());
    }