A related thread was created a few years back…
… however, the issue still persists. When you have Coda create an interactive filter for a Date column, one of the options in it is “Everything”. By it’s name, it should show you rows that have no value in the Date column, however it doesn’t.
I edited the filter’s formula to add “OR [the column].isBlank()” and that was enough to get me both what I match on and the blank ones. Still not ideal as when I want to see just the “past month”, I’ll also see the rows with now value for that column.
The fix here is to just make Everything mean, well, everything. Since Coda creates the filter for me, and the corresponding formula, I see it as a bug.