in src/main/scala/com/gu/ssm/utils/attempt/Attempt.scala [68:75]
def onComplete[B](callback: Either[FailedAttempt, A] => B)(implicit ec: ExecutionContext): Unit = {
this.asFuture.onComplete {
case util.Failure(e) =>
throw new IllegalStateException("Unexpected error handling was bypassed")
case util.Success(either) =>
callback(either)
}
}