Update by merging documents

The update API also support passing a partial document, which will be merged into the existing document (simple recursive merge, inner merging of objects, replacing core "keys/values" and arrays). For example:

UpdateRequest updateRequest = new UpdateRequest("index", "type", "1")
        .doc(jsonBuilder()
            .startObject()
                .field("gender", "male")
            .endObject());
client.update(updateRequest).get();