Blank option in filter. But where is it coming from?

Question

I created two custom columns in Date table and they return True or False values.

There are no blank values in either of these two columns in the Date table.

However, when I use these columns as filters, there appear to be Blank options.

Selecting and displaying the blank values returns results. Where are these blank values coming from?

Answer 1

Blank means you have values in the many side table of your relationship which do not exist on the one side table of your relationship.