Issue 6637: defaultdict.copy() failed with an empty factory.
diff --git a/Misc/NEWS b/Misc/NEWS
index a9cb534..289ee1d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -70,6 +70,10 @@
 Library
 -------
 
+- Issue #6637: defaultdict.copy() did not work when the default factory
+  was left unspecified.  Also, the eval/repr round-trip would fail when
+  the default_factory was None.
+
 - Issue #1424152: Fix for httplib, urllib2 to support SSL while working through
   proxy. Original patch by Christopher Li, changes made by Senthil Kumaran.