A null grav suite was a type of zero gravity environment available to travelers as special accommodations on transport ships.
In 2370, Lieutenant Commander Data accessed the commercial transport database and searched the passenger manifests of the ships SS Manoa, SS Kogin, and SS Wisconsin to find proof that Juliana O'Donnell traveled with his father Noonien Soong to Mavala IV in 2328.
According to the database, in 2328, Robert Levinson and Hilary Groner, who traveled from Denkir Orbital City to Janus VI, both requested null gravity accommodations on the Kogin. (TNG-R: "Inheritance", okudagram)