From 01469303ab53ff49026d0c9c26aa1e9c5c87d437 Mon Sep 17 00:00:00 2001
From: GRiker <griker@hotmail.com>
Date: Sun, 2 Jan 2011 11:53:03 -0700
Subject: [PATCH] GwR patch for empty merge field

---
 src/calibre/library/catalog.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/calibre/library/catalog.py b/src/calibre/library/catalog.py
index f013477308..c91c6bca88 100644
--- a/src/calibre/library/catalog.py
+++ b/src/calibre/library/catalog.py
@@ -4829,6 +4829,8 @@ class EPUB_MOBI(CatalogPlugin):
                 addendum = self.__db.get_field(record['id'],
                                             self.__merge_comments['field'],
                                             index_is_id=True)
+                if addendum is None:
+                    addendum = ''
                 include_hr = eval(self.__merge_comments['hr'])
                 if self.__merge_comments['position'] == 'before':
                     merged = addendum