what reason does Romeo give to Balthasar for going to Juliet's vault?

Romeo says that he must go grieve for Juliet and wants to take "a precious ring" or her wedding ring from her finger. Some people have said that, although Juliet does give Romeo a ring by way of the nurse inviting Romeo to Juliet's bed, Romeo and Juliet did not exchange rings and so Juliet does not have a ring of Romeo's and he has no "dear employment" for it. He makes this up to get rid of Balthazar.