All bonds issued under the provisions of this chapter must have endorsed thereon a statement to the effect that the same do not constitute an obligation of the state of North Dakota, the state board of higher education, nor the individual members, officers, or agents thereof, nor of the institution upon the campus of which the building or campus improvement is located, and that the said bonds are payable solely and only out of the revenues to be produced and received from the operation of said building or campus improvement. Such bonds must be submitted to the attorney general of North Dakota for examination and when such bonds have been examined and certified as legal obligations by the attorney general in accordance with such requirements as the attorney general may make, are incontestable in any court in this state unless suit thereon is brought in a court having jurisdiction thereof within thirty days from the date of such approval. Bonds so approved by the attorney general are prima facie valid and binding obligations according to their terms and the only defense which may be offered thereto in any suit instituted after such thirty-day period has expired is forgery, fraud, or violation of the constitution.