Description 

When a board used as an issue source for a plan is deleted, Jira throws a 500 error: 

2026-06-19 11:43:2: Error while adding issue sources to JQL, stacktrace=java.lang.RuntimeException: Error while adding issue sources to JQL at com.atlassian.rm.jpo.issueloading.jql.JqlQueryGenerator.addIssueSources(JqlQueryGenerator.java:187) [?:?] at com.atlassian.rm.jpo.issueloading.jql.JqlQueryGenerator.addClause(JqlQueryGenerator.java:104) [?:?]

The Jira code calls JqlQueryGenerator.addIssueSources, which tries to add a clause representing one of the issue sources. However, instead of adding a valid clause, it adds a null value and calls DefaultJqlClauseBuilder.addClause(null). This behavior is hardcoded in the Jira source code. The same issue does not occur when you delete a filter or a project used as an issue source.

Feature Request

We need to add validation that allows users to access the plan even if the board has been deleted. The 500 error should be handled gracefully, so that users can still access the plan and add a new issue source.