diff -r 54ff2789d75e -r c8411fb5dfef mercurial/context.py
--- a/mercurial/context.py	Wed Jul 23 11:16:22 2014 -0500
+++ b/mercurial/context.py	Wed Jul 16 13:07:39 2014 -0500
@@ -1577,7 +1577,7 @@
         files = sorted(set(files))
         self._status = [files, [], [], [], []]
         self._filectxfn = filectxfn
-        self.substate = None
+        self.substate = {}
 
         self._extra = extra and extra.copy() or {}
         if self._extra.get('branch', '') == '':