Here are some examples of how you can use nullify:
Because the other party didn’t honour the conditions, the contract is nullified.
In the US, individual states can nullify a federal law if they think it’s unconstitutional.
When a couple gets a divorce, they nullify their marriage vows.
The referee nullified the goal, because the footballer had touched the ball with his hands.
Pouring water on a burn is the nullification of it.
When the jury acquits a person when they do believe this person is guilty of an illegal act, this is jury nullification.