I have a calculated column made to show how many days overdue is a permit. Right now if the permit expiry date is not picked it is giving 44,265 days overdue due to the date being 12/31/1904. I want to put if isblank "" but I am not sure where to insert that in the code.

=IF(ISERROR(DATEDIF((Permit Expiry Date],Today,"d")),"0",(DATEDIF((Permit Expiry Date],Today,"d")))