@Internal
    protected Function<HttpContext, HttpClientContext> contextAdaptor() {
        return HttpClientContext::castOrCreate;
    }
Adds to the list of {@link Closeable} resources to be managed by the client.
<p>
For internal use.
</p>
httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpClientBuilder.java