I'm using the jira-ext plugin for jenkins, and try to update custom fields (in JIRA) of type Label and User Picker (single user) as part of my build. The update fails on the Label update stating:

net.rcarz.jiraclient.JiraException: Field expects an Iterable value

And on the User Picker, error:

net.rcarz.jiraclient.RestException: 400 Bad Request: {"errorMessages":[],"errors":{"customfield_10100":"data was not an object"}}

The configuration I use to update both is attached as a screenshot.

What is the correct format to update such custom fields through this plugin? I tried matching the JIRA REST API documentation but probably didn't get that exactly.