--- a/mercurial/context.py	Wed Jun 03 13:45:42 2015 -0400
+++ b/mercurial/context.py	Wed Jun 03 13:51:27 2015 -0400
@@ -251,6 +251,9 @@
     def sub(self, path):
         return subrepo.subrepo(self, path)
 
+    def nullsub(self, path, pctx):
+        return subrepo.nullsubrepo(self, path, pctx)
+
     def match(self, pats=[], include=None, exclude=None, default='glob',
               listsubrepos=False):
         r = self._repo