How do I search for objects for which a certain field is empty? (Zoho CRM API)

Hi,

I'm trying to use the " searchRecords" method of Zoho CRM API.

I see that it supports operators like "AND" and "OR".

But how do I search for objects for which a certain field is empty?

Couldn't find anything like NOTEMPTY() operator in the docs.

Thanks in advance!