diff --git a/src/main/java/org/ntlab/citrusserver/repositories/TodoManager.java b/src/main/java/org/ntlab/citrusserver/repositories/TodoManager.java
index 95f3f4b..db1a1df 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/TodoManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/TodoManager.java
@@ -204,6 +204,9 @@
         if(bookManager.getBooks(accountId) == null){
             return null;
         }
+        if(bookManager.getBook(accountId, bookId) == null){
+            return null;
+        }
         if(!todos.containsKey(accountId)){
             todos.put(accountId, new HashMap<>());
         }