Slicer that accounts with blank dates

Hello!

I have a cases table which has a 'close date'. I then created a date table like that:

CloseDateTable =
CALENDAR(MIN('cases'[dateClosed]), MAX('cases'[dateClosed]))

I did the relationship (1:M) and put the date table as a slicer. It works fine, but it ignores the blank values. The rows on the cases table that have a blank value on closed date means the case is still open and I'd like to show them.

I tried:
-'show items with no data' on the slicer, it doesn't work
- adding a blank row to the CloseDateTable, but then it doesn't allow me to do a relationship with the cases table - even though is only one row it says it has duplicate values

I'm stuck, any alternatives on how I can achieve this?

Thank you so much!

Grazi