I am trying to write a script to calculate values if there are null values in a table however it never calculates any values and I am pretty sure my code is right.Where (Operator) is a field with values and null valuesand (PointID) is a field with coded values and the Operator name as a 3 letter code stored within the text. Expression: Calc (!Operator!) Code Block: def Calc (Operator): while (Operator is null): if (re.search ("DWS", PointID) is TRUE): return "Don" elif (re.search ("GMS", PointID) is TRUE): return "Gordon" elif (re.search ("JZL", PointID) is TRUE): return "Julian" elif (re.search ("AWM", PointID) is TRUE): return "Anthony" else return (Operator)