fun <T : Any> tag(type: KClass<T>): T? = type.java.cast(tags[type])

  /**
   * Returns the tag attached with `Object.class` as a key, or null if no tag is attached with
   * that key.
   *
   * Prior to OkHttp 3.11, this method never returned null if no tag was attached. Instead it
   * returned either this request, or the request upon which this request was derived with
   * [newBuilder].
   *