In the absence of clear and convincing evidence to the contrary, language in a governing instrument granting a trustee discretion to make or withhold a distribution shall prevail over any language in the governing instrument indicating that the beneficiary may have a legally enforceable right to distributions or indicating a standard for payments or distributions.
Iowa Code § 633A.4702
2004 Acts, ch 1015, §30 2005 Acts, ch 38, §54