[Modify] Replace it

websocket-sharp/WebSocket.cs

@@ -2145,8 +2145,8 @@ namespace WebSocketSharp
     /// </summary>
     public void Close ()
     {
-      var msg = _readyState.CheckIfAvailable (true, true, false, false);
-      if (msg != null) {
+      string msg;
+      if (!checkIfAvailable (true, true, false, false, out msg)) {
         _logger.Error (msg);
         error ("An error has occurred in closing the connection.", null);