Is it normal to suck on your girlfriends nipples to fall asleep?

Wasn't sure where to post this, so I hope here is fine.

My girlfriend asked me out of nowhere why I never suck on her nipples to fall asleep. I was confused and told her that I'm not an infant any more and I don't really need that to fall asleep. She told me that this is something her ex-boyfriend used to always do which I personally find very weird. I told her that this doesn't sound like normal behaviour to me but she felt like I was just being defensive and refuse to be vulnerable and 'less masculine'.

Which is why I just wanted to know if this behaviour is in fact 'normal' or at least common.