Nothing in this act shall invalidate or restrict any other or additional right or remedy available to sales representatives or preclude sales representatives from seeking to recover in one action on all claims against a principal. The provisions of this act may not be waived. In applying the provisions of this act, the courts of this Commonwealth shall not recognize any purported waiver of the provisions of this act, whether by express waiver or by attempt to make a contract or agreement subject to the laws of another state.