Как посчитать общий вес?

public static class Box {
   List<Stuff> sfuff
   List<Box> boxes;
}

public static class Stuff {
    int weight;
}

public static int weight(Box box) {
  if (box.stuff== null && box.boxes == null || box == null) {
    return 0;
  }  
  int weight;
  if (box.boxes != null) {        
      for (Box b : box.boxes) {
          weight += weight(b);
      }        
  }
  for (Stuff s : box.stuff) {
      weight += s.weight;
  }
 
  return weight;
}

import java.util.Arrays;
import java.util.List;
 
public class Helper {
 
    public static void main(String[] args) {
        Box box1 = new Box();
        System.out.println(weight(box1));
        Box box2 = new Box();
        box2.sfuffList = Arrays.asList(new Stuff());
        box2.sfuffList.get(0).weight = 1;
        box2.boxList = Arrays.asList(new Box());
        box2.boxList.get(0).sfuffList = Arrays.asList(new Stuff());
        box2.boxList.get(0).sfuffList.get(0).weight = 1;
        System.out.println(weight(box2));
 
    }
 
    public static class Box {
        List<Stuff> sfuffList;
        List<Box> boxList;
    }
 
    public static class Stuff {
        int weight;
    }
 
    public static int weight(Box box) {
        if (box == null) {
            return 0;
        }
        else if (box.sfuffList == null && box.boxList == null) {
            return 0;
        }
        else if (box.sfuffList != null && box.boxList == null) {
            return box.sfuffList.stream().mapToInt(s -> s.weight).sum();
        }
        return box.sfuffList.stream().mapToInt(s -> s.weight).sum() +
                box.boxList.stream().mapToInt(Helper::weight).sum();
    }
}