From 62c78290c156f3225f32a721107a2cd8e6035416 Mon Sep 17 00:00:00 2001
From: Charles Haley <cbhaley@i.wont.say.com>
Date: Mon, 24 Feb 2014 18:44:35 +0100
Subject: [PATCH] Allow the empty string when writing to bool custom columns.
 Bulk edit uses the empty string for None, at least in this case.

---
 src/calibre/db/write.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/calibre/db/write.py b/src/calibre/db/write.py
index 175b484c91..7dd278fa57 100644
--- a/src/calibre/db/write.py
+++ b/src/calibre/db/write.py
@@ -94,7 +94,7 @@ def adapt_bool(x):
             x = True
         elif x == 'false':
             x = False
-        elif x == 'none':
+        elif x == 'none' or x == '':
             x = None
         else:
             x = bool(int(x))