as long as it's PLAIN or unsweetened water, don't worry
night time training is NOT a skill to learn it is a body hormone that the body has to develop, so cup or not it will either happen or not happen. (YOU can drink a cup of water right before bed and not have to get up and pee because you have a hormone telling your body to not pee in the middle of the night.) Daytime potty train and then at night just use pull ups. Honestly it's not a big deal.
If it's NOT just plain water in the sippy then gradually make it watered down until it is all water. (the first night 3 oz flavor to 1 oz plain, second day 2 and 2, third night 3 plain to 1 flavor - that kind of thing).
For those that mentioned cavities - it is true - I was under doctor's orders to give my daughter milk (with carnation instant breakfast and heavy cream in it) if she woke in the middle of the night. If I didn't she literally lost weight overnight. And she was already in the later stages of starvation, so not an option of stopping. She had to have 5 teeth pulled when she was 6 to 8 years old cause they were destroyed at the gum line, not normal cavities. But in my case we knew that was the risk but death or teeth pulling was not a choice, now was it?