236.48  Bonds may be validated; validity of bonds.--When an issue of bonds for any school district shall be authorized in the manner provided under the terms of this chapter, such bonds shall, in the discretion of the school board, be subject to validation in the manner provided for in chapter 75. In lieu of validation as set forth in that chapter, the school board may, in its discretion, submit to the Department of Legal Affairs all information relating to the issuance of bonds as provided in said chapter 75, and an approving opinion of the Department of Legal Affairs shall be sufficient evidence that the bonds are valid. Bonds reciting that they are issued pursuant to the terms of this chapter shall, in any action or proceeding involving their validity, be conclusively deemed to be fully authorized thereby, to have been issued, sold, executed, and delivered in conformity therewith, and with all other provisions of law applicable thereto, and shall be incontestable, anything herein or in other statutes to the contrary notwithstanding, unless such action or proceeding is begun before or within 30 days after the date upon which the bonds are sold, paid for and delivered.