diff -r f1af59451c0c -r 5f162f61e479 mercurial/graphmod.py
--- a/mercurial/graphmod.py	Sat Jan 03 20:16:10 2009 +0100
+++ b/mercurial/graphmod.py	Sun Jan 04 19:10:42 2009 +0100
@@ -26,6 +26,9 @@
       - The changeset date/time
     """
 
+    if start_rev == nullrev and not stop_rev:
+        return
+
     assert start_rev >= stop_rev
     assert stop_rev >= 0
     curr_rev = start_rev