this is because you have not formulated the right question, as the agent Spooner in I robot, dear.
Consider this other formulation: 'What is the difference between return (); and return [];?' For completness you have to know there is also return {}; that returns a reference to an anonymous hash.
HtH L*
There are no rules, there are no thumbs..
Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.