Looks like my issues were due to the fact that the getAvailableRooms method didn't handle correctly getFirstRoomResult when it was null.
That's why I was getting java.lang.NullPointerException.
Also, no sense in opening a chat window until the URL is ready to be sent.
I'm attaching two patches.
OpenmeetingsPluginMenuItem.java.diff (1.61 KB)
OpenmeetingsPluginSoapClient.java.diff (1004 Bytes)