The personal representative, trustee, or any affected beneficiary under a will, trust, or other instrument of a decedent who dies or did die after December 31, 2009, and before January 1, 2011, may bring a proceeding to determine the decedent's intent when the will, trust, or other instrument contains a formula that is based on the federal estate tax or generation-skipping tax. The proceeding must be commenced within twelve months following the death of the decedent.