From 224d35cb79f7f0d0edffbc08633809abafd3dd27 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sun, 7 Jul 2019 09:11:59 +0530
Subject: [PATCH] EPUB Output: If there are no guide elements do not output an
 empty guide tag. Makes the asinine epubcheck happy. Fixes #1835560 [epub file
 fails at epub check](https://bugs.launchpad.net/calibre/+bug/1835560)

---
 src/calibre/ebooks/oeb/base.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index 4cbf29d75e..24560c49d7 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -1486,6 +1486,8 @@ class Guide(object):
         return elem
 
     def to_opf2(self, parent=None):
+        if not len(self):
+            return
         elem = element(parent, OPF('guide'))
         for ref in self.refs.values():
             attrib = {'type': ref.type, 'href': urlunquote(ref.href)}