Handle null values for messages number

Author: germanosin

api/src/main/java/io/kafbat/ui/controller/TopicsController.java

@@ -362,7 +362,10 @@ private Comparator<InternalTopic> getComparatorForTopic(
       case OUT_OF_SYNC_REPLICAS -> Comparator.comparing(t -> t.getReplicas() - t.getInSyncReplicas());
       case REPLICATION_FACTOR -> Comparator.comparing(InternalTopic::getReplicationFactor);
       case SIZE -> Comparator.comparing(InternalTopic::getSegmentSize);
-      case MESSAGES_NUMBER ->  Comparator.comparing(InternalTopic::getMessagesNumber);
+      case MESSAGES_NUMBER ->  Comparator.comparing(
+          InternalTopic::getMessagesNumber,
+          Comparator.nullsLast(Long::compareTo)
+      );
       default -> defaultComparator;
     };
   }