Before passing a parameter, you must create a variable of the correct .NET data type. If you want to pass the ABL Unknown value (?) (null in .NET) for .NET value types (System.Boolean, System.Decimal, System.Int32, System.Int64, and System.DateTime), you must use the corresponding holder object. The ABL to .NET mappings are the same as the ones defined for passing parameters to Open Client proxy methods. For more information on the supported mappings between ABL and .NET data types, see Data Type Mappings for Parameters.