“To avoid summary judgment by raising an affirmative defense, the non-movant must do more than merely plead the affirmative defense.” Singleton v. Elliott, No. 14-13-00040-CV, 2014 WL 1922260, at *3 (Tex. App. May 13, 2014) (citing Lujan v. Navistar Fin. Corp., No. 01–12–00740–CV, 2014 WL 1328191, at *4 (Tex.App.-Houston [1st Dist.] April 3, 2014, no pet.)