mercurial/context.py

--- a/mercurial/context.py	Mon Jun 15 16:50:31 2015 -0400
+++ b/mercurial/context.py	Sun Jun 14 22:04:17 2015 -0400
@@ -1334,6 +1334,9 @@
     def __contains__(self, key):
         return self._repo.dirstate[key] not in "?r"
 
+    def hex(self):
+        return "ff" * 20
+
     @propertycache
     def _parents(self):
         p = self._repo.dirstate.parents()