"match may not be exhaustive" on JsLookupResult

Play Framework
1

I’m in the process of upgrading from Scala 2.13.3 to 2.13.4. The most conspicuous change there is the tightening of exhaustivity checks, and most of those are straightforward. But I’m a bit stumped by this one.

I have a couple of blocks of code that are roughly:

json \ "thingy" match {
  case JsDefined(tpe) => tpe match {
    ...
  }
  case JsUndefined() => ... error value here
}

The Scala compiler is kicking out “match may not be exhaustive. It would fail on the following input: JsUndefined()”. Which is odd on the face of it, and I’m puzzled – there’s nothing obviously wrong with the definition of JsUndefined.unapply(). (It’s a little odd that it takes Object instead of JsLookupResult, but it looks like it should work.)

I found this on play-json 2.9.2, but it still seems to be true on 2.10.0-RC5.

Any thoughts? I can attach @unchecked to the match if need be, but the mystery is rankling.