Add tests for bug #478115, parsedate_tz() IndexError when a Date:
field exists with an empty value.
diff --git a/Lib/test/test_email.py b/Lib/test/test_email.py
index 6a66199..37ddc30 100644
--- a/Lib/test/test_email.py
+++ b/Lib/test/test_email.py
@@ -937,6 +937,9 @@
                 toff = time.timezone
             self.assertEqual(offset, toff)
 
+    def test_parsedate(self):
+        self.assertEqual(Utils.parsedate(''), None)
+
 
 
 # Test the iterator/generators