Filter by custom field not set

Posted on behalf of Eolinger. Original posting date 2017-06-05.

There is no API call to filter by custom fields that are not set, this seems to be an oversight because clearly the UI has this ability. I thought that the API was supposed to replicate the UI functionality but clearly that does not seem to be the case here. Can this feature be added to the feature request list as it would be helpful. The alternative, integrating through the entire collection of tasks to find the ones not set is highly inefficient for large databases.