non-null, but attempts to read its content will fail.
 *  New: Kotlin-specific APIs for request tags. Kotlin language users can lookup tags with a type
    parameter only, like `request.tag<MyTagClass>()`.
 *  New: MockWebServer has improved support for HTTP/1xx responses. Once you've migrated to the new
    `mockwebserver3` package, there's a new field, `MockResponse.informationalResponses`.