Are you really sure that the $iteratorDueDtSchedule_2/DueDt_Installment field is not empty? You should not only check that the object is there but also that the specific field is not empty.
Regards,
Ronald
When I specify != empty in the XPath constraint retrieving the list such as below, is that filtering for non-blanks on the field or object? Regardless, once I moved the addDays result to variable, the error went away. Thanks Ronald!
[DueDt_Installment != empty]