fix tests

src/server/services/websocket_service.py

@@ -84,12 +84,10 @@ class ConnectionManager:
             for room_members in self._rooms.values():
                 room_members.discard(connection_id)
             
-            # Remove empty rooms
-            self._rooms = {
-                room: members
-                for room, members in self._rooms.items()
-                if members
-            }
+            # Remove empty rooms (keep as defaultdict)
+            for room in list(self._rooms.keys()):
+                if not self._rooms[room]:
+                    del self._rooms[room]
             
             # Remove connection and metadata
             self._active_connections.pop(connection_id, None)
@@ -155,7 +153,7 @@ class ConnectionManager:
             connection_id: Target connection identifier
         """
         websocket = self._active_connections.get(connection_id)
-        if websocket:
+        if websocket is not None:
             try:
                 await websocket.send_json(message)
                 logger.debug(
@@ -237,7 +235,7 @@ class ConnectionManager:
         
         for connection_id in room_members:
             websocket = self._active_connections.get(connection_id)
-            if not websocket:
+            if websocket is None:
                 continue
                 
             try: