diff --git a/src/main/java/org/ntlab/citrusserver/repositories/ScheduleManager.java b/src/main/java/org/ntlab/citrusserver/repositories/ScheduleManager.java
index 313d487..7f6718d 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/ScheduleManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/ScheduleManager.java
@@ -141,12 +141,14 @@
     @Override
     public void bookDeleted(Account accountIn, Book book) {
         String account = accountIn.getId();
-        for (int year : schedules.get(account).keySet()) {
-            for (int month : schedules.get(account).get(year).keySet()) {
-                for (int day : schedules.get(account).get(year).get(month).keySet()) {
-                    for (int scheduleId : schedules.get(account).get(year).get(month).get(day).keySet()) {
-                        if (schedules.get(account).get(year).get(month).get(day).get(scheduleId).getBookId().equals(book.getBookId())) {
-                            schedules.get(account).get(year).get(month).get(day).get(scheduleId).setBookId(0);
+        if (schedules.containsKey(account)) {
+            for (int year : schedules.get(account).keySet()) {
+                for (int month : schedules.get(account).get(year).keySet()) {
+                    for (int day : schedules.get(account).get(year).get(month).keySet()) {
+                        for (int scheduleId : schedules.get(account).get(year).get(month).get(day).keySet()) {
+                            if (schedules.get(account).get(year).get(month).get(day).get(scheduleId).getBookId().equals(book.getBookId())) {
+                                schedules.get(account).get(year).get(month).get(day).get(scheduleId).setBookId(0);
+                            }
                         }
                     }
                 }