--- a/mercurial/templater.py	Thu Sep 28 21:00:01 2006 +0100
+++ b/mercurial/templater.py	Fri Sep 29 18:17:29 2006 -0700
@@ -356,7 +356,7 @@
         self.write(thing, header=True)
 
     def show(self, rev=0, changenode=None, brinfo=None, changes=None,
-             copies=None, **props):
+             copies=[], **props):
         '''show a single changeset or file revision'''
         log = self.repo.changelog
         if changenode is None: