diff --git a/src/main/java/org/ntlab/citrusserver/repositories/PublicBookManager.java b/src/main/java/org/ntlab/citrusserver/repositories/PublicBookManager.java
index bde074a..f8cc181 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/PublicBookManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/PublicBookManager.java
@@ -113,7 +113,12 @@
             case 1:
                 ArrayList<BookForSort> booksForSort = new ArrayList<>();
                 for(Book book : books){
-                    booksForSort.add(new BookForSort(book, favoriteManager.getFavorited(book.getAccountId(), book.getBookId()).size()));
+                    HashSet<String> favorites = favoriteManager.getFavorited(book.getAccountId(), book.getBookId());
+                    int count = 0;
+                    if(favorites != null){
+                        count = favorites.size();
+                    }
+                    booksForSort.add(new BookForSort(book, count));
                 }
                 booksForSort.sort(Comparator.comparing(BookForSort::favoriteNum).reversed());
                 ArrayList<Book> res = new ArrayList<>();