California Code, Code of Civil Procedure - CCP § 1094

If no return be made, the case may be heard on the papers of the applicant. If the return raises only questions of law, or puts in issue immaterial statements, not affecting the substantial rights of the parties, the court must proceed to hear or fix a day for hearing the argument of the case.

If a petition for a writ of mandate filed pursuant to Section 1088.5 presents no triable issue of fact or is based solely on an administrative record, the matter may be determined by the court by noticed motion of any party for a judgment on the peremptory writ.