do you think this is more clear? I can't seem to find a clear way to express this:

```
      val v = (summedDelta, storedValue) match {
        case (Some((_, delta)), Some(sv)) => extSemigroup.get.plus(sv, delta)
        case (Some((_, delta)), None) => delta
        case (None, Some(sv)) => sv
        case _ => sys.error("This should never happen, both summedDelta and storedValue were None")
      }
```