When you say "you don't have to get me anything", what do you expect?

"You don't have to get me anything." When I say it I mean you really don't have to get me anything. However, I saw a movie and the girl told the guy he didn't need to get her anything. The guy didn't and the girl got upset. Now ignoring the movies, what do you expect when you say this to your boyfriend/girlfriend?
When you say "you don't have to get me anything", what do you expect?
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