Do both and reference the ticket in the comment (something like "// TODO: deal properly with NULLs here, see Jira://PRJ-123" with the ticket going into as much extra detail as it relevant).
That way someone looking at the code can see that it is not in its intended final form rather than having to intuit the fact from other clues or knowing every ticket in the work list. Particularly useful if trying to find/diagnose a bug that may be caused/worsened/highlighted by the code in question. Also works in reverse: of the ticket doesn't give accurate location information for the related code you can search for the ticket ID and find where you should start looking from the comments.
That way someone looking at the code can see that it is not in its intended final form rather than having to intuit the fact from other clues or knowing every ticket in the work list. Particularly useful if trying to find/diagnose a bug that may be caused/worsened/highlighted by the code in question. Also works in reverse: of the ticket doesn't give accurate location information for the related code you can search for the ticket ID and find where you should start looking from the comments.