A lease of a building executed pursuant to RCW 35.42.010 through 35.42.090 may grant the lessee city or town an option to renew for a further term on like conditions, or an option to purchase the building covered by the lease at any time prior to the expiration of the term. A lease with an option to purchase shall provide that all sums paid as rent up to the time of exercising the option shall be credited toward the payment of the purchase price as of the date of payment. No lease shall provide, nor be construed to provide, that any city or town shall be under any obligation to purchase the leased building.