Any written agreement entered into between a city and the owner of land proposed to be annexed by the city which conditions the delivery or extension of municipal water, sewer, electrical, gas or other services to the land, regardless of the size of the land, on the consent of the owner to annexation on a later date shall be deemed to be a sufficient consent to annexation under Kan. Stat. Ann. § 12-520, and amendments thereto, by the owner and any successors in interest. Such agreements shall be filed by the city in the office of the register of deeds of the county where the land is located within 30 days after being executed by all parties. Any such agreement executed prior to the effective date of this act shall be binding upon the owner and any successors in interest if the agreement is filed by the city in the office of the register of deeds of the county where the land is located within 180 days following the effective date of this act; however, the failure to so file any written agreement within 180 days shall not make such agreement void or otherwise unenforceable.