Merge pull request DSpace#9069 from tdonohue/fix_cannot_index_site

Fix "Site cannot be indexed" error which appears in ITs and sometimes in logs

dspace-api/src/main/java/org/dspace/discovery/IndexEventConsumer.java

@@ -154,7 +154,11 @@ public void consume(Context ctx, Event event) throws Exception {
 
             case Event.REMOVE:
             case Event.ADD:
-                if (object == null) {
+                // At this time, ADD and REMOVE actions are ignored on SITE object. They are only triggered for
+                // top-level communities. No action is necessary as Community itself is indexed (or deleted) separately.
+                if (event.getSubjectType() == Constants.SITE) {
+                    log.debug(event.getEventTypeAsString() + " event triggered for Site object. Skipping it.");
+                } else if (object == null) {
                     log.warn(event.getEventTypeAsString() + " event, could not get object for "
                                  + event.getObjectTypeAsString() + " id="
                                  + event.getObjectID()