code: public URI proxy(URI uri) {
          Proxy conf;
          String scheme;
  
          scheme = uri.getScheme();
          conf = proxies.get(scheme);
          if (conf == null || conf.excludes(uri)) {
              return null;
          }
          try {
              return new URI(scheme, null, conf.host, conf.port, null, null, null);
          } catch (URISyntaxException e) {
              throw new IllegalArgumentException(e);
          }
      }
docs: return proxy url if configured for this filesystem: