So your code calls a function that is named in a way that indicates it might return a set or an integer (and its parameters make sense in both situations), then

So your code calls a function that is named in a way that indicates it might return a set or an integer (and its parameters make sense in both situations), then you take the return value and add() to it ambiguously, and then you do nothing else with it? You don't loop over it or query it for set membership or pass it to any functions or multiply it? This is exactly the point of the article. Extremely extremely unlikely. But if you have a real world example of this, I'm sure the article's author is interested.