Collection (or Map) relationships and null

[Dain Sundstrom]

When I access a collection (or Map) valued relation field when will  
the field value be null and when won't it be null?  In CMP 2, it was  
gaurenteed that the field was always non-null, but I'd expect with  
OpenJPA that it is at least null form new() to em.persist().

Also, what happens when someone puts a bad value on the Collection  
(or Map).  For example, a null in the collection, or an entry in the  
map where the pk doesn't match the bean added.

-dain