We're looking update how we auto opt-in subscribers to fulfillment emails they're paying to receive. If a subscriber is new or renews, we want to auto opt-into the fulfillment newsletters UNLESS they've manually requested to opt-out via their preference center.
Currently all newsletters in our preference center are managed by boolean fields in a form, which do not allow for a NULL value. I'm considering changing them to string fields that display a checkbox. The string would allow "yes, no, null" values in the field. This would help in the trigger campaign opting in users, and leaving preferences as is if the value is "no".
Trigger = subscription date updated
Change data value, if newsletter preference is "yes or null" to = "yes"
Any thoughts on using a string field vs boolean? Possible changes I should think thru? I've reviewed Josh Hill's Building a Full Subscription Center in Marketo - Marketing Rockstar Guides and multiple community threads, but didn't see anything on my question.