Any trust or plan heretofore or hereafter created for the purposes and of the type enumerated in section 48-2002, whether in real or personal property or in both real and personal property, may continue in perpetuity or for such time as may be necessary to accomplish the purposes of the trust or plan. Such trust or plan shall not be invalid as violating any statute or rule of law against perpetuities, against accumulations of earnings, concerning the suspension of the power of alienation of the title to property, or otherwise limiting the duration of trusts or agreements.