If it appears from the face of the [unlawful detainer] complaint that the plaintiff is an improper plaintiff, a demurer will lie. If it is not apparent from the face of the complaint, the issue must generally be raised as an affirmative defense in the answer.The fact that a plaintiff is not a proper plaintiff would appear on the face of the complaint, for example, when• The complaint states that the landlord has sold the property; or• The name of the plaintiff is not the same as the name of the landlord on the lease attached to the complaint, and the plaintiff does not allege that he or she is the successor in interest.