From c5320420a933495b6e02dff873bb1d397768174c Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Mon, 19 Jul 2021 21:12:26 +0530
Subject: [PATCH] HTML Input: Fix the presence of BookDesigner markup causing
 conversion to fail. Fixes #1936792 [Html conversion
 BookTitle](https://bugs.launchpad.net/calibre/+bug/1936792)

---
 src/calibre/ebooks/conversion/preprocess.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/calibre/ebooks/conversion/preprocess.py b/src/calibre/ebooks/conversion/preprocess.py
index e3e6983742..f6ef3d295e 100644
--- a/src/calibre/ebooks/conversion/preprocess.py
+++ b/src/calibre/ebooks/conversion/preprocess.py
@@ -452,7 +452,7 @@ def book_designer_rules():
         (re.compile('<span[^><]*?id=subtitle[^><]*?>(.*?)</span>', re.IGNORECASE|re.DOTALL),
         lambda match : '<h3 class="subtitle">%s</h3>'%(match.group(1),)),
     ]
-    return None
+    return ans
 
 
 class HTMLPreProcessor(object):