What should evaluating an empty block (`EVAL []`) do?

[hostilefork]

@rgchris

I notice that Ren-C (in R3C as well as current) does vaporize in the case of reduce [( )] which to mind is the same thing.

That actually arises from a more universal rule about GROUP!:

"groups just group things, they don't synthesize values of their own."

I tried changing eval [] to be void (and related places where empty blocks had to have an answer) and I don't really see any particularly obvious bad side to it. Nothing crashed.