From ca0a977b09a8c1e4a55a7dd9785a77375203f3aa Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 4 Feb 2022 16:41:08 +0530
Subject: [PATCH] Better handling of empty prefix list

---
 src/calibre/ebooks/metadata/__init__.py | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/calibre/ebooks/metadata/__init__.py b/src/calibre/ebooks/metadata/__init__.py
index 1a62f8eaaa..9ee0054b63 100644
--- a/src/calibre/ebooks/metadata/__init__.py
+++ b/src/calibre/ebooks/metadata/__init__.py
@@ -163,12 +163,15 @@ def get_title_sort_pat(lang=None):
         ans = frozenset(ans) if ans is not None else frozenset(data['eng'])
     except Exception:
         ans = frozenset((r'A\s+', r'The\s+', r'An\s+'))
-    ans = '|'.join(ans)
-    ans = '^(%s)'%ans
-    try:
-        ans = re.compile(ans, re.IGNORECASE)
-    except:
-        ans = re.compile(r'^(A|The|An)\s+', re.IGNORECASE)
+    if ans:
+        ans = '|'.join(ans)
+        ans = '^(%s)'%ans
+        try:
+            ans = re.compile(ans, re.IGNORECASE)
+        except:
+            ans = re.compile(r'^(A|The|An)\s+', re.IGNORECASE)
+    else:
+        ans = re.compile('^$')  # matches only the empty string
     _title_pats[lang] = ans
     return ans