From ae81ae2b7230e0615d269779a60bd9c67be0d659 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Mon, 5 Jul 2021 10:35:09 +0530
Subject: [PATCH] Handle passing None to unicode_normalize

---
 src/calibre/db/annotations.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/calibre/db/annotations.py b/src/calibre/db/annotations.py
index fa695e3075..83be2e3d65 100644
--- a/src/calibre/db/annotations.py
+++ b/src/calibre/db/annotations.py
@@ -12,8 +12,10 @@ no_cfi_sort_key = cfi_sort_key('/99999999')
 
 
 def unicode_normalize(text):
-    from unicodedata import normalize
-    return normalize('NFKC', text)
+    if text:
+        from unicodedata import normalize
+        text = normalize('NFKC', text)
+    return text
 
 
 def bookmark_sort_key(b):