Validation error on datefield after update to 8.4.0

Have just updated from 8.3.1 to 8.4.0 and PHP 8.0 to 8.1.

After the update when I try to edit a record and save with a Blank Date type field I get a validation error and it will not allow the save if the date field is blank.

When I create a new record it saves with a blank date field, but if subsequently try to edit and save I get the validation error because the Date type field is blank.

This issue does not arise with a Date and Time Type field - they will still save after edit blank.

Any suggestions why/how to get around this validation error without entering a date?