§ 5-1111. Execution by agent in real property transactions; written authorization required. If executed by an agent, any agreement, promise, undertaking, assignment or offer required by section 5-1103, 5-1105, 5-1107 or 5-1109 to be in writing, which affects or relates to real property or an interest therein in any manner stated in subdivisions one or two of section 5-703 of this chapter, shall be void unless such agent was thereunto authorized in writing.