This bug was originally marked as duplicate of bug 178935, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.

Build: NetBeans IDE Dev (Build cdev-2017-on-100211)
VM: Java HotSpot(TM) 64-Bit Server VM, 14.3-b01-101, Java(TM) SE Runtime Environment, 1.6.0_17-b04-248-9M3125
OS: Mac OS X

User Comments:
juhrik: open already opened chatroom causes this exception

juhrik: In the list of chatrooms doubleclick one that is already opened and the AssertionError appears.

juhrik: In chat window when I double click on a chatroom in the list of the first tab then the proper chatroom opens as another tab. When I doubleclick on the same item in the list again then the exception appears.




Stacktrace: 
java.lang.AssertionError: Chat room anagram-game@muc.kenai.com already joined
   at org.netbeans.modules.kenai.collab.chat.KenaiConnection.join(KenaiConnection.java:247)
   at org.netbeans.modules.kenai.collab.chat.ChatPanel.<init>(ChatPanel.java:408)
   at org.netbeans.modules.kenai.collab.chat.ChatTopComponent.setActiveGroup(ChatTopComponent.java:319)
   at org.netbeans.modules.kenai.collab.chat.GroupListItem.openChat(GroupListItem.java:93)
   at org.netbeans.modules.kenai.collab.chat.ContactList.contactJListMouseClicked(ContactList.java:290)
   at org.netbeans.modules.kenai.collab.chat.ContactList.access$200(ContactList.java:64)