Calculated Date Column. 31.12.1899 instead of nothing or hyphen

Hi,

There is a SharePoint list with 4 columns: Document / ExpirationDate / DaysBeforeExpiration / ReminderDate.

ReminderDate is the calculated column and shows the date, when a reminder is sent.
Formula: = ExpirationDate minus DaysBeforeExpiration

Some documents have no expiration date so there is no value included in this column. Then it shows a result like this: 28.12.1899. But it should show nothing or a hyphen instead.

Thanks for you help in advance.