diff -r a1e70c1dbec0 -r 1f30cbac34b6 mercurial/bundle2.py
--- a/mercurial/bundle2.py	Tue Oct 17 12:38:13 2017 +0200
+++ b/mercurial/bundle2.py	Tue Oct 17 15:39:34 2017 +0200
@@ -301,6 +301,8 @@
         self.captureoutput = captureoutput
         self.hookargs = {}
         self._gettransaction = transactiongetter
+        # carries value that can modify part behavior
+        self.modes = {}
 
     def gettransaction(self):
         transaction = self._gettransaction()