Synonyms for Null (same or very similar meaning)
WordNet sense 1 (a quantity of no importance):
aught, cipher, naught, nil, nix, nothing, zilch, zip, cypher, nada, zero, goose egg, zippoWordNet sense 2 (lacking any legal or binding force):
voidWordNet sense 3 (having no cogency or legal force):
invalid, invalidFrom the ODE community, based on WordNetadd/edit