diff -r 8ea51e9e7031 -r 3da456d0c885 mercurial/revlog.py
--- a/mercurial/revlog.py	Mon Nov 22 17:57:11 2010 +0100
+++ b/mercurial/revlog.py	Mon Nov 22 18:15:58 2010 +0100
@@ -212,7 +212,7 @@
             return None
         self.mapfind_count += 1
         last = self.l - 1
-        while self.index[last] != None:
+        while self.index[last] is not None:
             if last == 0:
                 self.all = 1
                 self.allmap = 1