N.J. Stat. Ann. § 2A:66-5

In any proceeding in lieu of prerogative writ instituted by the attorney general, by virtue of his office, to ascertain by what right a person holds any public office, he shall, at the trial, prove affirmatively all the facts alleged in the complaint and not admitted in the answer. The defendant shall not be required to offer evidence until such facts are proven, and then only to controvert the same.