public static LookupResult empty() {
        return EMPTY_LOOKUP_RESULT;
    }
@Test
    public void serializeEmpty() {
        final LookupResult lookupResult = LookupResult.empty();
        final JsonNode node = objectMapper.convertValue(lookupResult, JsonNode.class);

        assertThat(node.isNull()).isFalse();
        assertThat(node.path("single_value").isNull()).isTrue();
        assertThat(node.path("multi_value").isNull()).isTrue();
        assertThat(node.path("ttl").asLong()).isEqualTo(Long.MAX_VALUE);
    }