I'm able to retrieve tasks for a workspace assigned to a particular assignee - using curl:
curl -u <api_key>: "https://app.asana.com/api/1.0/tasks?workspace=14916&assignee=me"
However I'd like to be able to search for not just "me" or an id of a user - but "Nobody" as you are able to do in the web interface.
curl -u <api_key>: "https://app.asana.com/api/1.0/tasks?workspace=14916&assignee=Nobody"
Results in an error returned by the server:
assignee: Not an email, ID, or "me": Nobody
Is there an id for "Nobody" that I can use here?
This is currently not supported. We're working on designing a way to expose the power of the Advanced Search in the API, but it's still early in the design phase. We have internal integrations that (for instance) look at a project and find all the unassigned incomplete tasks, but the way we do it is to get all the incomplete tasks (?completed_since=now) and then filter out the ones with assignees on the client. That's obviously not what we'd like to be doing, and there's no way to do it for an entire workspace.
So all I can say it that it's high on our list of API priorities to support this, but we don't yet. Sorry :-(