Empty date comparison

Hello everyone,
I'm stuck on a topic about dates.
I have a field where I ask for the date of birth, if the date of birth is not known then we go blank since it is not blocking and we ask him for the reasons and we end the questionnaire.
how in the "RELEVANT" put the condition.
I tried this formula but it shows an error:
${datenais} = date(' ')

Thanks for your help !

I would suggest doing the following flow, if it can work for you.

Is the date of birth known?
Yes / No

[if "yes"] Please select the date of birth.
(date picker)

[if "no"] What is the reason the data of birth is not known?


Have you tried just this?

${datenais} = ''

Basically, dates are stored internally in the XForm data as strings, so you just need to check if it is an empty string (!)
Have a play around with this form:
emptydate.xlsx (5.8 KB)


Thank you very much danbjoseph and Xiphware, for your reactions. it helps me a lot.
But the formula:
${datenais} = ' ' does not work for me.
thank you !

Can you please try the above form, and perhaps provide more detail about in what way it is not working for you, thanks.