private ElasticsearchBackend backend() {
    return backend(1024);
  }
Should be greater than default elastic {@code size} which is 10.
@see <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-from-size.html">from-size</a>
criteria/elasticsearch/test/org/immutables/criteria/elasticsearch/ScrollingTest.java