What do I say exactly?

My father in law messages me asking If we have any needs or wants for my son's birthday and you might think this is really sweet but we have a very bad relationship with my wife's parents very unsupportive and very abusive when we lived there last year, my mother in law did things behind our back that was really mentally abusing and stalker related. It was my worst experience living with someone like them. Honestly I don't want anything but if I say no thank you, they will think I'm being rude. No matter what I say, they will find it somehow offensive.