Antonyms for the phrase "rendered null and void" would include terms that represent validity, effectiveness, and enforceability. Examples of such words would be "valid," "effective," "enforceable," "binding," and "legitimate." These terms imply that the action or decision in question has legal or official standing and is not subject to being set aside or declared void. Additionally, antonyms could include words that indicate the opposite of null and void, such as "established," "successful," "recognized," "accepted," and "supported." Overall, antonyms for "rendered null and void" suggest the opposite of an unsuccessful or overturned action or decision.