public static Retrofit defaultRetrofit(OkHttpClient client, ObjectMapper mapper) {
        return new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .client(client)
                .addConverterFactory(JacksonConverterFactory.create(mapper))
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();
    }
Shuts down the OkHttp ExecutorService.
The default behaviour of OkHttp's ExecutorService (ConnectionPool)
is to shut down after an idle timeout of 60s.
Call this method to shut down the ExecutorService immediately.
service/src/main/java/com/theokanning/openai/service/OpenAiService.java