Retrofit retrofit = new Retrofit.Builder()
    .baseUrl("https://api.github.com")
    .addConverterFactory(GsonConverterFactory.create(gson))
    .addCallAdapterFactory(new ErrorHandlingExecutorCallAdapterFactory(new ErrorHandlingExecutorCallAdapterFactory.MainThreadExecutor()))
    .build();

GitHubService service = retrofit.create(GitHubService.class);