N.J. Stat. Ann. § 46:4-6

A covenant by the grantor in a deed "that he has done no act to encumber the said lands" , shall have the same effect as if he covenanted that he had not done or executed, or knowingly suffered to be done or executed, any act, deed or thing whereby the lands and premises conveyed, or intended so to be or any part thereof, are or will be changed, charged, altered, affected, defeated, or encumbered in title, estate or otherwise.