Do not send empty alarm updated messages during creation of TS subscriptions

application/src/main/java/org/thingsboard/server/service/subscription/TbAlarmDataSubCtx.java

@@ -177,7 +177,9 @@ public class TbAlarmDataSubCtx extends TbAbstractDataSubCtx<AlarmDataQuery> {
                 alarm.getLatest().computeIfAbsent(keyType, tmp -> new HashMap<>()).putAll(latestUpdate);
                 return alarm;
             }).collect(Collectors.toList());
-            wsService.sendWsMsg(sessionId, new AlarmDataUpdate(cmdId, null, update, maxEntitiesPerAlarmSubscription, data.getTotalElements()));
+            if (!update.isEmpty()) {
+                wsService.sendWsMsg(sessionId, new AlarmDataUpdate(cmdId, null, update, maxEntitiesPerAlarmSubscription, data.getTotalElements()));
+            }
         } else {
             log.trace("[{}][{}][{}][{}] Received stale subscription update: {}", sessionId, cmdId, subscriptionUpdate.getSubscriptionId(), keyType, subscriptionUpdate);
         }