Versions are stored in lists. Documentation on how to work with lists can be found here.
You can access the whole version by issue?.versions[0] and issue?.fixVersions[0] which returns a Version object, issue?.versions (and issue?.fixVersions) will return a list of objects.
Read
Page properties
id
1
Returned value
True if the first (fix)version has been released, false otherwise. If no (fix) versions are availbale, null is returned.