From d24835bff8f297330b81870c2576e34b909a6a0f Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sun, 21 Oct 2012 18:39:13 +0530
Subject: [PATCH] ...

---
 src/calibre/gui2/convert/regex_builder.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/calibre/gui2/convert/regex_builder.py b/src/calibre/gui2/convert/regex_builder.py
index 3ce8ac36d5..f3c1f0a826 100644
--- a/src/calibre/gui2/convert/regex_builder.py
+++ b/src/calibre/gui2/convert/regex_builder.py
@@ -211,6 +211,9 @@ class RegexEdit(QWidget, Ui_Edit):
         self.button.clicked.connect(self.builder)
 
     def builder(self):
+        if self.db is None:
+            self.doc_cache = _('Click the Open button below to open a '
+                    'ebook to use for testing.')
         bld = RegexBuilder(self.db, self.book_id, self.edit.text(), self.doc_cache, self)
         if bld.cancelled:
             return