Does a general demurrer in a declaratory relief action need to be sustained on appeal?

(20) Assuming the foregoing adequately alleges the existence of an actual, present controversy subject to declaratory relief, plaintiffs are not thereby necessarily entitled to relief on appeal. "`Strictly speaking, a general demurrer is not an appropriate means of testing the merits of the controversy in a declaratory relief action because plaintiff is entitled to a declaration of his rights even if it be adverse.' [Citations.] However, `where the issue is purely one of law, if the reviewing court agreed with the trial court's resolution of the issue it would be an idle act to reverse the judgment of dismissal for a trial on the merits. In such cases the merits of the legal controversy may be considered on an appeal from a judgment of dismissal following an order sustaining a demurrer without leave to amend and the opinion of the reviewing court will constitute the declaration of the legal rights and duties of the parties concerning the matter in controversy.'" (Herzberg v. County of Plumas (2005) 133 Cal.App.4th 1, 24 [34 Cal.Rptr.3d 588].)