Switch labels (null again), some tweaking

[Maurizio Cimadamore]

>>
>> If I read the rules correctly, Box(Soup) + Bag(Soup) "cover" 
>> Container<Lunch>, with the exception of the { null, Box(null), 
>> Bag(null) }. So the above will throw when `lunch` is null, and will 
>> also throw with Box(null) or Bag(null). Correct?
>>
>
> Correct (under the "we make switches total" plan.)

I realized there's also another remainder Box/Bag(*) - e.g. 
Box/Bag(Pizza), where Pizza is a new type that shows up in the sealed 
hierarchy.

To cover that (not that it's required at compile-time, just to imagine 
what javac would emit), we need probably one of these:

case Box b:

or

case Container c

Right?

Maurizio