Agreed that this is confusing, but ultimately I guess this is down to the fact that e.g `5` simply is also a valid `Unit`?
```
scala> val five: Unit = 5
<console>:7: warning: a pure expression does nothing in statement position; you
may be omitting necessary parentheses
       val five: Unit = 5
                        ^
five: Unit = ()
```

Given that, I'm not sure what more one could expect to do to ensure a "real" `Unit` is passed here?