From d0ea6b31c4a09304a11b5a075bc3bf6bd0ec0264 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sat, 21 Apr 2018 18:03:00 +0530
Subject: [PATCH] When updating EPUB 2 to EPUB 3 ensure only a single dc:date
 element is present in the OPF

---
 src/calibre/ebooks/metadata/opf_2_to_3.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/calibre/ebooks/metadata/opf_2_to_3.py b/src/calibre/ebooks/metadata/opf_2_to_3.py
index 14a53794e4..6d11fcb4ba 100644
--- a/src/calibre/ebooks/metadata/opf_2_to_3.py
+++ b/src/calibre/ebooks/metadata/opf_2_to_3.py
@@ -105,7 +105,10 @@ def upgrade_date(root, data):
     found = False
     for date in XPath('./opf:metadata/dc:date')(root):
         val = date.text
-        if val:
+        if not val:
+            remove_element(date, data.refines)
+            continue
+        if not found:
             found = True
             continue
         if not val or found:  # only one dc:date allowed