Sprint field showing 'None' causes confusion

Sprint field displays 'None' on view issue and issue navigator when an issue is only in completed sprints

Steps to Reproduce

• Create a sprint, with issues from the board backlog
• Complete the sprint

Results

• The sprint field value is displayed as 'none' for all the issues in the completed sprint, as long as the issue belongs to no other active sprint.

Symptoms
If you search for issues using the JQL below:

Sprint is not empty

There are results displayed with Sprint = None:

If we open one of such issues, we can see that although the field Sprint is None, the Agile section displays that the issue belonged to a sprint which was completed:

Expected result:
The sprint field should display the sprint in which the issue was included.