--- a/mercurial/bundlerepo.py	Fri Jun 30 03:28:28 2017 +0200
+++ b/mercurial/bundlerepo.py	Fri Jun 30 03:31:26 2017 +0200
@@ -414,7 +414,7 @@
     if create:
         raise error.Abort(_('cannot create new bundle repository'))
     # internal config: bundle.mainreporoot
-    parentpath = ui.config("bundle", "mainreporoot", "")
+    parentpath = ui.config("bundle", "mainreporoot")
     if not parentpath:
         # try to find the correct path to the working directory repo
         parentpath = cmdutil.findrepo(pycompat.getcwd())