California Code, Business and Professions Code - BPC § 19943.5

If a gambling enterprise conducts play of a controlled game that has been approved by the department pursuant to Section 19826, and the controlled game is subsequently found to be unlawful, so long as the game was played in the manner approved, the approval by the department shall be an absolute defense to any criminal, administrative, or civil action that may be brought, provided that the game is played during the time for which it was approved by the department and the gambling enterprise ceases play upon notice that the game has been found unlawful.  In any enforcement action, the gambling enterprise shall have the burden of proving the department approved the controlled game and that the game was played in the manner approved.