Date fields are never truly empty. They'll have a value of 0000-00-00 if nothing is selected. Will improve the checks in CB Conditional to take this into account when checking for empty condition. For now you should be able to use a condition like the following.
Is Empty:
Field: YOUR_DATE_FIELD
Operator: Equal To
Value: 0000-00-00
Is Not Empty:
Field: YOUR_DATE_FIELD
Operator: Not Equal To
Value: 0000-00-00
If it's a datetime field be sure to use 0000-00-00 00:00:00.
forge.joomlapolis.com/issues/8496