In the event that any mortgagee or its respective successor in title shall succeed to the interest of Landlord hereunder, the liability of such mortgagee or successor shall exist only so long as it is the owner of the Premises or any interest therein, or is the tenant under any ground or underlying lease referred to in Section 21.1 above. No additional rent or any other charge shall be paid more than ten (10) days prior to the due date thereof and payments made in violation of this provision shall (except to the extent that such payments are actually received by a mortgagee) be a nullity as against any mortgagee and Tenant shall be liable for the amount of such payments to such mortgagee.