diff -r a4d8de93023c -r 8843c9a8771b mercurial/changegroup.py
--- a/mercurial/changegroup.py	Sun Dec 12 20:01:05 2021 -0500
+++ b/mercurial/changegroup.py	Sun Dec 12 21:10:02 2021 -0500
@@ -350,10 +350,11 @@
 
             def ondupchangelog(cl, rev):
                 if rev < clstart:
-                    duprevs.append(rev)
+                    duprevs.append(rev)  # pytype: disable=attribute-error
 
             def onchangelog(cl, rev):
                 ctx = cl.changelogrevision(rev)
+                assert efilesset is not None  # help pytype
                 efilesset.update(ctx.files)
                 repo.register_changeset(rev, ctx)