Cal. Code of Civil Procedure § 475

The court must, in every stage of an action, disregard any error, improper ruling, instruction, or defect, in the pleadings or proceedings which, in the opinion of said court, does not affect the substantial rights of the parties. No judgment, decision, or decree shall be reversed or affected by reason of any error, ruling, instruction, or defect, unless it shall appear from the record that such error, ruling, instruction, or defect was prejudicial, and also that by reason of such error, ruling, instruction, or defect, the said party complaining or appealing sustained and suffered substantial injury, and that a different result would have been probable if such error, ruling, instruction, or defect had not occurred or existed. There shall be no presumption that error is prejudicial, or that injury was done if error is shown.