Neb. Rev. Stat. § 25-2163: Peremptory writ; when issued; failure to answer, effect; pleading new matter, effect.

If no answer be made, a peremptory mandamus must be allowed against the defendant. If an answer be made containing new matter, the same shall not in any respect conclude the plaintiff, who may, on the trial or other proceeding, avail himself of any valid objection to its sufficiency, or may countervail it by proof, either in direct denial or by way of avoidance.