When using stripe-java to get the expanded total_details.breakdown from checkout session, some fields inside discount are missing like id and promotion_code

main.java

package org.ricardoteixeira;

import com.stripe.Stripe;
import com.stripe.model.checkout.Session;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Main {
    public static void main(String[] args) {

        Stripe.apiKey = "sk_test_...";

        String session_id = "cs_test_...";

        List<String> expandList = new ArrayList<>();
        expandList.add("total_details.breakdown");

        Map<String, Object> params = new HashMap<>();
        params.put("expand", expandList);

        try {
            Session session = Session.retrieve(session_id, params, null);
            System.out.println(session.getTotalDetails().getBreakdown());
            // response:
            /*
              {
               "discounts": [
                {
                  "amount": 5000,
                  "discount": { // MISSING FIELDS LIKE promotion_code and id
                    "amount": null,
                    "discount": null,
                  }
                }
               ],
              "taxes": []
              }
            */
        } catch (com.stripe.exception.StripeException e) {
            e.printStackTrace();
        }
    }
}