JIRA Datacenter can share lucene index between nodes on request. In some cases this lucene index can be corrupted at specific node, in that case that node still can reply and propagate that index to other nodes (nodes copy it from shared folder), thus affecting whole cluster.
Potential "donor" node should detect that index is corrupted (and possibly not healthy) and should not reply to request.
There is similar check already in backupIndex(), see JRASERVER-64927
so node refuses to share index if it does't have index operations.