ForumLetterReceiver实现Serializable

letterbox/src/main/java/com/apobates/forum/letterbox/entity/ForumLetterReceiver.java

 package com.apobates.forum.letterbox.entity;
 
 import javax.persistence.Transient;
+import java.io.Serializable;
 
 /**
  * ForumLetter的收件人
@@ -8,7 +9,8 @@ import javax.persistence.Transient;
  * @author xiaofanku
  * @since 20200510
  */
-public class ForumLetterReceiver {
+public class ForumLetterReceiver implements Serializable {
+    private static final long serialVersionUID = 1L;
     private long member;
     private String memberNickname;