Using a formula on TYPE = DateTime format = ISO 8601 (UTC) blank = 50%

I have a schema (Mockaroo - Random Data Generator and API Mocking Tool | JSON / CSV / SQL / Excel) where I have a Field with a TYPE = DateTime format = ISO 8601 (UTC) blank = 50%. However when the resulting value is “blank” I want to change the value to 8 zeros (00000000).

I used the formula below and the result is that the date is fomarted as expected but I do not get zeros when the result is ‘blank’ - any ideas, thanks.
if this.nil? then “00000000” else this.strftime(’%Y%m%d’) end