Propertybase API - IN filter: empty option

Propertybase is a real estate solution for real estate agencies. You can use it to manage your property listings and sync the listings with your website via their API.

They have a nice simple API for fetching filtered property listings. However, it was unclear to me how to filter the listings by a field whose value is empty or set to a certain value.

The syntax for filtering by a field that is empty:

Fieldname__c=

The syntax for filtering by a field whose value is either test or unicorn:

Fieldname__c=IN(test;unicorn)

If you want to filter by a field whose value is empty, test or unicorn, you can do so by prepending an additional ; to your options:

Fieldname__c=IN(;test;unicorn)