Master calendar and selectable null dates?

[#1]

I have a table with 2 dates; OpenDate and CloseDate.

A null CloseDate means the record has not been closed yet.  I replace nulls with "Open" in the script.

I want Year, Month, and Day selection listboxes for CloseDate, with the ability to select "Open" if CloseDate is Null.

If I replace null CloseDates with 'Open' and join to a master calendar, I will get greyed out list boxes due to missing records since 'Open' is not a value in the master calendar.

If I create CloseDate_Year, CloseDate__Month, and CloseDate_Day within the table, then the listboxes may not contain every individual day.

Is there any way to get both every date, and selectable Open CloseDates?

[Gysbert_Wassenaar]

You can either add a dummy value to your master calendar to link it with the Open value from the CloseDate field or add a listbox for CloseDate and select Open in that listbox.