docs: @Override
      public CompletableFuture<Boolean> existsWebSocket(Serializable userid, @RpcTargetAddress InetSocketAddress targetAddress) {
          if (logger.isLoggable(Level.FINEST)) logger.finest(WebSocketNodeService.class.getSimpleName() + ".event: " + userid + " existsWebSocket from " + targetAddress);
          if (localEngine == null) return CompletableFuture.completedFuture(false);
          return CompletableFuture.completedFuture(localEngine.existsLocalWebSocket(userid));
      }