JIRA user Matt Doar reported as a comment in JRA-11702:

I also found another place where the Integrity Checker itself can die:

Caused by: java.lang.IllegalArgumentException: Cannot get schemes for null project
at com.atlassian.jira.scheme.AbstractSchemeManager.getSchemes(AbstractSchemeManager.java:105)
at com.atlassian.jira.workflow.DefaultWorkflowSchemeManager.getWorkflowScheme(DefaultWorkflowSchemeManager.java:76)
at com.atlassian.jira.workflow.OSWorkflowManager.getWorkflowName(OSWorkflowManager.java:86)
at com.atlassian.jira.workflow.OSWorkflowManager.getWorkflow(OSWorkflowManager.java:299)
at com.atlassian.jira.appconsistency.integrity.check.WorkflowCurrentStepCheck.getStepDesc(WorkflowCurrentStepCheck.java:287)
at com.atlassian.jira.appconsistency.integrity.check.WorkflowCurrentStepCheck.doCheck(WorkflowCurrentStepCheck.java:123)
... 55 more

The Integrity Checker should be as robust as possible given dodgy data. Investigate the cause of this and fix the Integrity Checker to handle it gracefully.