#vulnerable code 
                                @Override
    public Server choose(Object key) {
        WeightFilterEntity weightFilterEntity = weightRandomLoadBalance.getWeightFilterEntity();
        if (!weightFilterEntity.hasWeight()) {
            return super.choose(key);
        }

        List<Server> eligibleServers = getPredicate().getEligibleServers(getLoadBalancer().getAllServers(), key);

        try {
            return weightRandomLoadBalance.choose(eligibleServers, weightFilterEntity);
        } catch (Exception e) {
            return super.choose(key);
        }
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public Server choose(Object key) {
        WeightFilterEntity weightFilterEntity = weightRandomLoadBalance.getWeightFilterEntity();
        if (weightFilterEntity == null) {
            return super.choose(key);
        }

        if (!weightFilterEntity.hasWeight()) {
            return super.choose(key);
        }

        List<Server> eligibleServers = getPredicate().getEligibleServers(getLoadBalancer().getAllServers(), key);

        try {
            return weightRandomLoadBalance.choose(eligibleServers, weightFilterEntity);
        } catch (Exception e) {
            return super.choose(key);
        }
    }