fun build(): DnsOverHttps {
      val client = this.client ?: throw NullPointerException("client not set")
      return DnsOverHttps(
        client.newBuilder().dns(buildBootstrapClient(this)).build(),
        checkNotNull(url) { "url not set" },
        includeIPv6,
        post,
        resolvePrivateAddresses,
        resolvePublicAddresses,
      )
    }