fix npd

util/websocket.go

@@ -31,7 +31,9 @@ type WSChannel struct {
 
 // Close closed the channel.
 func (c *WSChannel) Close() {
-	c.Conn.Close()
+	if nil != c.Conn {
+		c.Conn.Close()
+	}
 }
 
 // Refresh refreshes the channel by updating its use time.