Remove all +1 moodlets based on trait buff?

I want to make a "stoic" trait as a gift for my sister. She has a character that is fairly neutral until a very strong emotion, which she'd like for the sim version as well. My thinking for this trait is to remove all +1 moodlets so that the sim will be just "fine" until they experience a +2 moodlet.

My question is... how do I make that possible? I know I should have a hidden buff ... and I know I should do something with blacklisting... but I don't know what. This is my first trait, so any pointers would be helpful.