new room may not be overwrite existing one

git-svn-id: https://svn.apache.org/repos/asf/mina/vysper/trunk@1347557 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/server/extensions/xep0045-muc/src/main/java/org/apache/vysper/xmpp/modules/extension/xep0045_muc/storage/InMemoryRoomStorageProvider.java b/server/extensions/xep0045-muc/src/main/java/org/apache/vysper/xmpp/modules/extension/xep0045_muc/storage/InMemoryRoomStorageProvider.java
index 522bbcc..bdde7b5 100644
--- a/server/extensions/xep0045-muc/src/main/java/org/apache/vysper/xmpp/modules/extension/xep0045_muc/storage/InMemoryRoomStorageProvider.java
+++ b/server/extensions/xep0045-muc/src/main/java/org/apache/vysper/xmpp/modules/extension/xep0045_muc/storage/InMemoryRoomStorageProvider.java
@@ -42,6 +42,8 @@
     }
 
     public Room createRoom(MUCFeatures mucFeatures, Entity jid, String name, RoomType... roomTypes) {
+        if (roomExists(jid)) throw new IllegalStateException();
+
         Room room = new Room(jid, name, roomTypes);
         room.setRewriteDuplicateNick(mucFeatures.isRewriteDuplicateNick());
         room.setMaxRoomHistoryItems(mucFeatures.getMaxRoomHistoryItems());