#vulnerable code 
                                public static Registration deserialize(JsonObject jObj) {
        Registration.Builder b = new Registration.Builder(jObj.getString("regId", null), jObj.getString("ep", null),
                new InetSocketAddress(jObj.getString("address", null), jObj.getInt("port", 0)).getAddress(),
                jObj.getInt("port", 0),
                new InetSocketAddress(jObj.getString("regAddr", null), jObj.getInt("regPort", 0)));
        b.bindingMode(BindingMode.valueOf(jObj.getString("bnd", null)));
        b.lastUpdate(new Date(jObj.getLong("lastUp", 0)));
        b.lifeTimeInSec(jObj.getLong("lt", 0));
        b.lwM2mVersion(jObj.getString("ver", "1.0"));
        b.registrationDate(new Date(jObj.getLong("regDate", 0)));
        if (jObj.get("sms") != null) {
            b.smsNumber(jObj.getString("sms", ""));
        }

        JsonArray links = (JsonArray) jObj.get("objLink");
        Link[] linkObjs = new Link[links.size()];
        for (int i = 0; i < links.size(); i++) {
            JsonObject ol = (JsonObject) links.get(i);

            Map<String, Object> attMap = new HashMap<>();
            JsonObject att = (JsonObject) ol.get("at");
            for (String k : att.names()) {
                JsonValue jsonValue = att.get(k);
                if (jsonValue.isNumber()) {
                    attMap.put(k, jsonValue.asInt());
                } else {
                    attMap.put(k, jsonValue.asString());
                }
            }
            Link o = new Link(ol.getString("url", null), attMap);
            linkObjs[i] = o;
        }
        b.objectLinks(linkObjs);
        Map<String, String> addAttr = new HashMap<>();
        JsonObject o = (JsonObject) jObj.get("addAttr");
        for (String k : o.names()) {
            addAttr.put(k, o.getString(k, ""));
        }
        b.additionalRegistrationAttributes(addAttr);

        return b.build();
    } 
                            #location 16 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public static Registration deserialize(JsonObject jObj) {
        Registration.Builder b = new Registration.Builder(jObj.getString("regId", null), jObj.getString("ep", null),
                IdentitySerDes.deserialize(jObj.get("identity").asObject()),
                new InetSocketAddress(jObj.getString("regAddr", null), jObj.getInt("regPort", 0)));
        b.bindingMode(BindingMode.valueOf(jObj.getString("bnd", null)));
        b.lastUpdate(new Date(jObj.getLong("lastUp", 0)));
        b.lifeTimeInSec(jObj.getLong("lt", 0));
        b.lwM2mVersion(jObj.getString("ver", "1.0"));
        b.registrationDate(new Date(jObj.getLong("regDate", 0)));
        if (jObj.get("sms") != null) {
            b.smsNumber(jObj.getString("sms", ""));
        }

        JsonArray links = (JsonArray) jObj.get("objLink");
        Link[] linkObjs = new Link[links.size()];
        for (int i = 0; i < links.size(); i++) {
            JsonObject ol = (JsonObject) links.get(i);

            Map<String, Object> attMap = new HashMap<>();
            JsonObject att = (JsonObject) ol.get("at");
            for (String k : att.names()) {
                JsonValue jsonValue = att.get(k);
                if (jsonValue.isNumber()) {
                    attMap.put(k, jsonValue.asInt());
                } else {
                    attMap.put(k, jsonValue.asString());
                }
            }
            Link o = new Link(ol.getString("url", null), attMap);
            linkObjs[i] = o;
        }
        b.objectLinks(linkObjs);
        Map<String, String> addAttr = new HashMap<>();
        JsonObject o = (JsonObject) jObj.get("addAttr");
        for (String k : o.names()) {
            addAttr.put(k, o.getString(k, ""));
        }
        b.additionalRegistrationAttributes(addAttr);

        return b.build();
    }