nullifier

/ˈnʌləˌfaɪər/
noun
  1. A person or thing that makes something legally invalid or void.
    • The new law is a nullifier of previous tax exemptions.
    • The senator was known as a nullifier of outdated regulations.
    • The court acted as a nullifier of the unfair contract.
  2. A person or thing that causes something to have no effect or power.
    • This chemical is a nullifier of strong odors.
    • The shield acted as a nullifier of the enemy's radar signals.
    • She was a nullifier of negativity in the office, always calming tensions.