--- a/mercurial/cmdutil.py	Sun Dec 13 18:06:24 2009 +0100
+++ b/mercurial/cmdutil.py	Sun Dec 13 18:06:24 2009 +0100
@@ -651,7 +651,7 @@
             return 1
         return 0
 
-    def show(self, ctx, copies=(), **props):
+    def show(self, ctx, copies=None, **props):
         if self.buffered:
             self.ui.pushbuffer()
             self._show(ctx, copies, props)