Is it valid to conditionally suspend the revocation of *tadbir* based on a future event?

Primary text

If a master institutes *tadbir* on his slave and subsequently states, 'If she enters the house, I have revoked my *tadbir* upon her,' this declaration is invalid. Revocation of *tadbir* cannot be validly made conditional upon an event. Similarly, the statement, 'Every time she gives birth to a child, I have revoked my *tadbir* concerning it,' is invalid for the same reason.