The Adjutant General shall purchase, out of any funds appropriated by the Legislature for such purpose, an adequate public liability insurance covering all members of the organized militia while operating any land motor vehicle possessed or maintained by the organized militia: Provided, That no policy or contract of public liability insurance providing coverage for public liability shall be purchased as provided herein, unless it shall contain a provision or endorsement whereby the company issuing such policy waives, or agrees not to assert as a defense to any claim covered by the terms of such policy, the defense of governmental immunity. In any action against the Adjutant General, his officers, agents or employees, in which there is in effect liability insurance coverage in an amount equal to or greater than the amount sued for, the attorney for such Adjutant General, the attorney for such insurance carrier, or any other attorney who may appear on behalf of the Adjutant General, his agents, officers or employees shall not set up the defense of governmental immunity in any such action. Notwithstanding any other provision of this section, under no circumstances whatever shall the jury in any such action be advised directly or indirectly of the existence of any such insurance or of the amount thereof.