Currently, a status cannot be deleted from the statuses list (Jira Administration > Issues > Statuses) if it is used by workflows. However, it can be removed even if it exists in the issue history. Consequently, the status remains in the "changeitem" table, but is no longer present in the "issuestatus" table. This inconsistency results in any issue containing the orphan status in its history being inaccessible from the customer portal, leading to the following error in the catalina log:

java.lang.NullPointerException: Cannot invoke "com.atlassian.jira.issue.status.Status.getId()" because "status" is null

A missing status could also cause the last approvers' list not to be visible, an issue that is described in the article Last Approvers not being displayed after statusworkflow change.

Preventing users from deleting statuses that are present in the issue history or in the past approvals would mitigate this type of problems.