https://github.com/scala/scala-java8-compat/blob/62d4f80cc18d47aa32a08c8711d67565cf00d743/src/main/scala/scala/compat/java8/FutureConverters.scala#L66 ```scala def toJava[T, U <: T ](f: Future[U]): CompletionStage[T] = { ```
