Antonyms for the phrase "declared null and void" could include validated, confirmed, established, authorized, and approved. When something is declared null and void, it means that it has been deemed invalid or worthless, and its legal or authoritative status is stripped away. In contrast, the antonyms suggest that the subject in question has been shown to be legitimate, reliable, and supported by some form of authority or evidence. These antonyms can be useful when describing legal or important documents, contracts, or agreements that have undergone official approval or review, and are recognized as binding and enforceable.