fix

virgo.file/src/main/java/com/bosshand/virgo/file/model/Node.java

@@ -1,7 +1,10 @@
 package com.bosshand.virgo.file.model;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
+
 import java.io.Serializable;
 
+@JsonInclude(JsonInclude.Include.NON_NULL)
 public class Node implements Serializable{
 
 	/**