but the case subsequently becomes non-justiciable, the court retains certain limited au thority to dispose of the case by dismissal. See Travelers Ins. Co. v. Joachim, B15 S.W.3d 860, 865 (Tex.2010). If the district court lacks jurisdiction in any of these senses, then its decision does not bind the parties. Gomez, 891 S.W.2d at 245. “[A] decision that does not bind the parties is, by definition, an advisory opinion prohibited by Texas law.” Id. Immunity from liability is an affirmative defense, as opposed to immunity from suit, which deprives a court of subject matter jurisdiction ab initio. See Miranda, 138 S.W.3d at 224. Thus, “[¡Immunity from liability and immunity from suit are two distinct principles.” Tex. Dep’t. of Transp. v. Jones, 8 S.W.3d 636, 638 (Tex.1999) (per curiam) (<HOLDING>). Immunity from liability does not protect a
holding that affirmative defenses are waived if not pled holding that mitigation of damages is an affirmative defense that must be pleaded holding that like other affirmative defenses to liability immunity from liability must be pleaded or else it is waived holding that a claim of exemption is an affirmative defense which must be specifically pleaded holding immunity from liability is not jurisdictional