type declaration was nullable to support rare cases like the body on `Response.cacheResponse`,
    `Response.networkResponse`, and `Response.priorResponse`. In such cases the body is now
    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>()`.