Safe navigation operator (&.) for nil
foo&.bar is shorthand for foo && foo.bar, so what would you expect the result of the expression nil && nil.nil? to be?
This is because nil&.nil? is shorthand for nil && nil.nil?. This would evaluate to nil && true, which is then nil.
(nil && x).nil? always evaluates to true, for any value of x.
While the syntax has power, this specific case has some potential to become a 'gotcha' for a developer:
(stuff&.things).nil? => This produces true if stuff doesn't exist, or stuff.things returns nil.
vs. the below case:
stuff&.things&.nil? => This produces nil in every case except the case where stuff.things returns something other than nil, in which case it would return false.
Because of the difficulty in normal boolean logic of differentiating between false and nil, it is unlikely that this would make sense in normal logic.