1
general::
Canceled, invalid, as in The lease is now null and void. This phrase is actually redundant, since null means "void," that is, "ineffective." It was first recorded in 1669.
American Heritage Idioms
2
general::
Phrase(s): null and void
Cliché without legal force; having no legal effect. • The court declared the law to be null and void. • The millionaire’s will was null and void because it was unsigned.
McGrawhill's American Idioms And Phrasal Verbs