322.10  Release from liability.--Any person who has signed the application of a minor for a driver's license may thereafter file with the department a verified written request that the license of said minor so granted be canceled. Thereupon, the department shall cancel the license of that minor, and the person who signed the application of such minor shall be relieved from liability imposed under this chapter by reason of having signed that minor's application for any subsequent negligence or willful misconduct of such minor in operating a motor vehicle.