#vulnerable code 
                                @Override
    public Set keys() {
        Set<byte[]> keys = JedisUtil.getJedis().keys(new String("*").getBytes());
        Set<Object> set = new HashSet<Object>();
        for (byte[] bs : keys) {
            set.add(SerializableUtil.unserializable(bs));
        }
        return set;
    } 
                            #location 3 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public Set keys() {
        Set<byte[]> keys = Objects.requireNonNull(JedisUtil.getJedis()).keys("*".getBytes());
        Set<Object> set = new HashSet<Object>();
        for (byte[] bs : keys) {
            set.add(SerializableUtil.unserializable(bs));
        }
        return set;
    }