How to remove that bargaining unit id from the assignment using HDL

Summary:

We have a requirement to download payslips for over 3000 plus employees for a period of time. None of the attributes available in the Filtered list meets our requirement to identify the population. So we tried to repurpose bargaining unit field which we are not using for this purpose. I was able to assign Bargaining unit to a sample of employees using HDL and the download of Documents worked fine. But now I am not able to remove that bargaining unit id from the assignment using HDL. The HDL runs to access and no errors, but the bargaining unit