Unable to reset settings to default

After changing the setting “Minimum available date” to an actual date, I can’t find a way to reset this back to NULL (ie the default behaviour of always using today as the minimum date).

If I clear the input and save, the previous date that was entered remains.

I believe this affects all the settings:

“Booking window closed time”
“Minimum available date”
“Maximum available date”

Please make it possible to clear these settings back to default.