Is it possible to pass null field value on API

I'm in need to fetch data from where a field value is not null.

In details I have to fetch all users whose department_id is null using our standard API. I was trying something like below but it wasn't worked:

`http://prettus.local/users?search=department_id:&searchFields=department_id:<>`

I'm curious whether it is possible, can someone help me out?