--- a/mercurial/patch.py	Mon Jun 26 15:46:24 2017 +0200
+++ b/mercurial/patch.py	Fri Jun 30 09:07:24 2017 -0700
@@ -448,6 +448,9 @@
     def exists(self, fname):
         raise NotImplementedError
 
+    def close(self):
+        raise NotImplementedError
+
 class fsbackend(abstractbackend):
     def __init__(self, ui, basedir):
         super(fsbackend, self).__init__(ui)