DMN17 — B-FEEL semantic precision for null values in collections

B-FEEL does not define the behavior when encountering null in a "for expression", a "quantified expression" (some, every) and a "comparison" using the "in" keyword.

The following are not covered by B-FEEL and should:

for x in null return x
some x in null satisfies x>0
every x in null satisfies x>0
1 in null