responses returned by OkHttp itself, and it was an old mistake to permit
    application code to omit a message.

 *  The challenge's scheme and realm are now non-null. If you are calling
    `new Challenge(scheme, realm)` you must provide non-null values. These were
    never null in challenges created by OkHttp, but could have been null in
    application code that creates challenges.

 *
 *  * http://host
 *
 * Both the unnecessary port specification (`:80`) and the absent trailing slash (`/`) cause URI to
 * bucket the two URLs separately. This harms URI's usefulness in collections. Any application that
 * stores information-per-URL will need to either canonicalize manually, or suffer unnecessary
 * redundancy for such URLs.
 *

 * ```
 *
 * ## Shutdown Isn't Necessary
 *
 * The threads and connections that are held will be released automatically if they remain idle. But
 * if you are writing a application that needs to aggressively release unused resources you may do
 * so.
 *
 * Shutdown the dispatcher's executor service with [shutdown()][ExecutorService.shutdown]. This will