--- a/mercurial/unionrepo.py	Sat Apr 14 09:23:48 2018 -0700
+++ b/mercurial/unionrepo.py	Sat Apr 14 09:57:44 2018 -0700
@@ -231,7 +231,7 @@
     def getcwd(self):
         return pycompat.getcwd() # always outside the repo
 
-def instance(ui, path, create):
+def instance(ui, path, create, intents=None):
     if create:
         raise error.Abort(_('cannot create new union repository'))
     parentpath = ui.config("bundle", "mainreporoot")