Okay, so search-members can only return people who have specific values you enter. There's not a way to search for a blank or null value. Instead I would recommend utilizing lists/members and segmenting what's returned:
http://apidocs.mailchimp.com/api/2.0/lists/members.phpAlso there isn't a "city" field in MailChimp. Instead there are "text" fields you can label "City", and there are "address" fields which can accept all of the different elements of an address separately (street, city, state, zip, etc.).
If you're using a text field labelled City, then finding people who have no value for this field will be touchy. If they used a MailChimp signup form and simply didn't fill that info out, you can find them by segmenting for a blank string "". If they were added before the field was created and never had the chance to enter a value there, their value is essentially "null" and there's no way to search/segment by a null value in the list.
If you're looking for an *empty* element of an address field (like they've entered a street but not a city), that's not going to be possible. You can only segment by a completely empty address field string as described above. If you're trying to find people whose address is missing a specific value, I would recommend testing out "contains/does not contain" options (ops):
http://apidocs.mailchimp.com/api/2.0/lists/segment-test.phpWe're working to put more segmenting/searching functionality for blank values into MailChimp soon, but in the meantime, working with an external database of your subscribers' information may be a more efficient way to determine the kind of data each may be missing.
-- Anna
On Tuesday, February 18, 2014 8:37:47 AM UTC-5, Kevin Turner wrote: