QueryConverter.prettyPrintJson method need enable serializeNulls

[maxid]

    private static String prettyPrintJson(final String json) {
        Gson gson = new GsonBuilder().setPrettyPrinting().create();
        JsonParser jp = new JsonParser();
        JsonElement je = jp.parse(json);
        return gson.toJson(je);
    }

changed to

    private static String prettyPrintJson(final String json) {
        Gson gson = new GsonBuilder().serializeNulls().setPrettyPrinting().create();
        JsonParser jp = new JsonParser();
        JsonElement je = jp.parse(json);
        return gson.toJson(je);
    }