--- a/mercurial/configitems.py	Tue Oct 09 23:26:35 2018 +0200
+++ b/mercurial/configitems.py	Wed Oct 10 00:21:02 2018 +0200
@@ -329,6 +329,9 @@
 coreconfigitem('devel', 'bundle2.debug',
     default=False,
 )
+coreconfigitem('devel', 'bundle.delta',
+    default='',
+)
 coreconfigitem('devel', 'cache-vfs',
     default=None,
 )