In selling or leasing its real property, a local agency shall first give any person who has occupied or used that property or a portion of it as a lawful tenant of the local agency for not less than 24 months during the 36 months next preceding the sale or lease, an opportunity to buy or lease the property at a reasonable price or rental, within a reasonable time after written notice to him; provided that occupancy or use of such property by an employee of such public agency shall create no rights hereunder.