public static ArmeriaRetrofitBuilder builder(WebClient baseWebClient) {
        requireNonNull(baseWebClient, "baseWebClient");
        checkArgument(!Clients.isUndefinedUri(baseWebClient.uri()),
                      "baseWebClient must have base URL.");
        return new ArmeriaRetrofitBuilder(baseWebClient);
    }
Returns a new {@link ArmeriaRetrofitBuilder} that builds a client that sends requests using
the specified {@link WebClient}.
retrofit2/src/main/java/com/linecorp/armeria/client/retrofit2/ArmeriaRetrofit.java