A transferee or creditor of a beneficiary shall not compel the trustee to pay any amount that is payable only in the trustee's discretion regardless of whether the discretion is expressed in the form of a standard of distribution, including, but not limited to, health, education, maintenance, and support, and whether such trustee is also a beneficiary. This Code section shall not apply to the extent of the proportion of trust property attributable to the beneficiary's contribution.