diff -r 640a0760e666 -r 634997248c97 mercurial/configitems.py
--- a/mercurial/configitems.py	Fri Jun 30 03:28:28 2017 +0200
+++ b/mercurial/configitems.py	Fri Jun 30 03:31:26 2017 +0200
@@ -63,6 +63,10 @@
 coreconfigitem('bookmarks', 'pushing',
     default=list,
 )
+# bundle.mainreporoot: internal hack for bundlerepo
+coreconfigitem('bundle', 'mainreporoot',
+    default='',
+)
 coreconfigitem('color', 'mode',
     default='auto',
 )