Field code
issue?.closedSprints?.map(s => s.name)

Closed sprints are stored in lists. Documentation on how to work with lists can be found here.

You can access the whole link by issue?.closedSprints[0] which returns an Issue object, issue?.closedSprints will return a list of objects.

Read

Returned valueThe list of names of all past sprints the issue belonged to.  If the issue is no Epic, null is returned.
Output data type

TEXT LIST

Example outputStart, MVP

If you still have questions, feel free to refer to our support team.