Any provision of a residential lease or rental agreement whereby a tenant, lessee, or occupant enters into a covenant, agreement or contract, the effect of which is to waive the benefits of any provision of this section, shall be against public policy and void; except that a covenant in any lease of two years' duration not counting any renewal periods, in which the tenant undertakes to make certain defined repairs or renovations in consideration for a substantially lower rent, shall not be against public policy nor void.