Where assets or rights present in a fiduciary estate are the subject of an agreement under which the settlor debtor retains the use or enjoyment of such assets or rights, no assignment or transfer of such assets or rights may be made to the fiduciary or to a third party by reason only of the opening of the proceedings, the adoption of the plan or a default in payment of a claim arising prior to the opening judgment. This prohibition applies on pain of nullity of the assignment or transfer.