Issue source page loads indefinitely when the plan is associated with a board with no filter

Issue Summary

When a board filter is deleted, if the related board is being used as an issue source for a plan, users will see a loading screen indefinitely when trying to edit the issue sources of the related plan.

Steps to Reproduce

1. Create a board
2. Create a plan, then add the created board as an issue source
3. Delete the filter that is associated with the board
4. Access the "Issue sources" page from the plan

Expected Results

All issue sources from the plan will be listed.

Actual Results

The issue sources page will show a spinning icon indefinitely, without displaying any content.

The following exception will appear at the atlassian-jira.log file:

2022-03-02 10:29:12,213+0000 http-nio-8080-exec-153 ERROR rrosa 127.0.0.1 /rest/jpo/1.0/plans/1/basicinfo [c.a.r.c.r.provider.exception.DefaultExceptionMapper] com.atlassian.rm.common.bridges.agile.AgileServiceOutcomeException: Could not get filter for board ID: 1
com.atlassian.rm.common.env.EnvironmentServiceException: com.atlassian.rm.common.bridges.agile.AgileServiceOutcomeException: Could not get filter for board ID: 1

Workaround

The solution provided at this KB article can be used for the affected board(s). Once they are associated with existing filters again, the issue sources page from the affected plan will be displayed as expected.