Establishment of rents between an owner and a tenant to whom this chapter is applicable shall hereafter be governed by the provisions of this chapter. No rent may be charged or collected for any apartment in excess of the ceiling rent which may be lawfully charged hereunder. No agreement between any owner and tenant shall be deemed to constitute a waiver by the tenant of any of his rights under this chapter. Any provision in any lease which shall provide for the payment of any amount of additional rent by virtue of any increase in any expense of the landlord, unless otherwise specifically authorized hereunder, shall be unenforceable, but shall not void the entire lease.