Graduation Gift

So, me and my dad don't have a good relationship. I don't remember the last time I saw him, the last time I do remember seeing him was when I graduated in 2015. I'm not too sure if i've seen him since then. Well, he has 3 kids from his wife (him and my mom are not together) and so one of his kids is graduating, my half brother. Because i don't talk to my dad I don't talk to that part of the family either. So i know nothing about my half brother. I'm not sure if I have to bring a gift or not and i wouldn't even know what to bring. For my graduation my dad got me flowers as a gift. There is going to be a dinner at a restaurant after the graduation, but I don't believe there's a graduation party. So should I just not bring a gift? or if I should what should I bring? any input is helpful!