#vulnerable code 
                             public static Instances createBootstrapSample(Instances instances) {
		Random rand = Random.getInstance();
		Map<Integer, Integer> map = new HashMap<>();
		for (int i = 0; i < instances.size(); i++) {
			int idx = rand.nextInt(instances.size());
			if (!map.containsKey(idx)) {
				map.put(idx, 0);
			}
			map.put(idx, map.get(idx) + 1);
		}
		Instances bag = new Instances(instances.getAttributes(), instances.getTargetAttribute(), map.size());
		for (Integer idx : map.keySet()) {
			int weight = map.get(idx);
			Instance instance = instances.get(idx).clone();
			instance.setWeight(weight);
			bag.add(instance);
		}
		return bag;
	} 
                            #location 9 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public static Instances createBootstrapSample(Instances instances) {
		Random rand = Random.getInstance();
		Map<Integer, Integer> map = new HashMap<>();
		for (int i = 0; i < instances.size(); i++) {
			int idx = rand.nextInt(instances.size());
			map.put(idx, map.getOrDefault(idx, 0) + 1);
		}
		Instances bag = new Instances(instances.getAttributes(), instances.getTargetAttribute(), map.size());
		for (Integer idx : map.keySet()) {
			int weight = map.get(idx);
			Instance instance = instances.get(idx).clone();
			instance.setWeight(weight);
			bag.add(instance);
		}
		return bag;
	}