Null and void
Definition 1 of 2
Pro Tip 1/3Legally Ineffective
Use 'null and void' to describe something with no legal power, like a contract that’s been cancelled. 
After the breach, their agreement is null and void.
Pro Tip 2/3Not Valid Anymore
It's used when something legal, like a rule or law, no longer applies or is no longer enforced. 
The previous zoning regulations are null and void.
Pro Tip 3/3Formal Phrase
'Null and void' is formal and most common in legal, official, or solemn contexts, not casual speech. 
The treaty was rendered null and void.