Why don't black people tip?

I work as a delivery driver for pizza hut and 80% black people dont tip me whreas all other races tip a lot better so why is that? I have been working here for over 2 years so I have observed long enough and I am getting less tips these days because a lot of black people are moving into my area. I hate delivering to blacks and so do all the other drivers at my store!!!! Get away from my place blacks!!!!!