Null references (oh no, not again!)

[BCS]

Hello Walter,

> Andrei suggests making a library type work for this rather than a
> language attribute, but it's still an extra thing that will have to be
> specified everywhere where used.
> 

I've considered trying to make a template that compile time enforces Non-null 
usage but can, with a version flag, be switched to a simple alias/typedef 
of the internal type. Near zero overhead and possibly just as strong a guard.