code: private Proxy lookupProxy(String hostKey, String portKey, Proxy.Type type, int defaultPort) {
          String host = System.getProperty(hostKey);
          if (host == null || host.isEmpty()) {
              return null;
          }
  
          int port = getSystemPropertyInt(portKey, defaultPort);
          return new Proxy(type, InetSocketAddress.createUnresolved(host, port));
      }
docs: Returns the proxy identified by the {@code hostKey} system property, or
  null.