fun proxy(proxy: Proxy?) =
      apply {
        if (proxy != this.proxy) {
          this.routeDatabase = null
        }
        this.proxy = proxy
      }

    /**
     * Sets the proxy selection policy to be used if no [proxy][proxy] is specified explicitly. The
     * proxy selector may return multiple proxies; in that case they will be tried in sequence until
     * a successful connection is established.
     *