On appeal from a dismissal after an order sustaining a demurrer, what is the test for determining whether a cause of action exists as a matter of law?

"On appeal from a dismissal after an order sustaining a demurrer, we review the order de novo, exercising our independent judgment about whether the complaint states a cause of action as a matter of law.... [Citations.] We deem to be true all material facts properly pled.... [Citation.] If no liability exists as a matter of law, we must affirm ... the judgment sustaining the demurrer." (Lazar v. Hertz Corp. (1999) 69 Cal.App.4th 1494, 1501, 82 Cal.Rptr.2d 368.)