@UnstableApi
    static RestClientBuilder builder(HttpPreprocessor httpPreprocessor) {
        requireNonNull(httpPreprocessor, "httpPreprocessor");
        return new RestClientBuilder(httpPreprocessor, null);
    }
Returns a new {@link RestClientBuilder} created with the specified {@link HttpPreprocessor}.
core/src/main/java/com/linecorp/armeria/client/RestClient.java