Note To Hollywood: Coffee Cups

I don't understand why every time we see a Starbucks-like coffee cup in a movie or TV show, it's so obviously empty. If they want it to be empty because they don't want to pick up sloshing audio then fine - it's silly but fine - but how hard would it be to still give it some mass. I mean, we can put Matt Damon on Mars but we can't figure out how to make a paper cup appear not empty?