mail: black wants to add this blank line stable

mail: black wants to add this blank line

I can't figure out how this got overlooked on previous runs, but here
we are. It looks like the culprit change is already public?

--- a/mercurial/mail.py	Wed Oct 30 16:29:45 2019 -0400
+++ b/mercurial/mail.py	Wed Oct 30 16:39:18 2019 -0400
@@ -445,6 +445,7 @@
         ep = email.parser.BytesParser()
         return ep.parsebytes(data)
 
+
 else:
 
     Generator = email.generator.Generator