[unity] EventSystem.current.IsPointerOverGameObject() reports a null pointer error solution

I encountered such a problem as EventSystem.current.IsPointerOverGameObject() a few days ago, as long as I trigger it, it will report a null pointer to me! ! I didn't touch this code at all at that time, but it just reported an error! ! ! I got stuck for ten hours! ! !
It was solved later, and I found out that it was because I deleted the EventSystem. I can't find a solution anywhere on the Internet! ! ! There is no forum outside the wall either! ! ! Tmd is such a thing! ! i want to blog