internal error string argument expaced got bytes

brz: ERROR: TypeError: string argument expected, got 'bytes'

Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/breezy/commands.py", line 1022, in exception_to_return_code
return the_callable(*args, **kwargs)
File "/usr/lib/python3/dist-packages/breezy/commands.py", line 1208, in run_bzr
ret = run(*run_argv)
File "/usr/lib/python3/dist-packages/breezy/commands.py", line 762, in run_argv_aliases
return self.run(**all_cmd_args)
File "/usr/lib/python3/dist-packages/breezy/commands.py", line 787, in run
return class_run(*args, **kwargs)
File "/usr/lib/python3/dist-packages/breezy/builtins.py", line 3768, in run
tree.commit(message_callback=get_message,
File "/usr/lib/python3/dist-packages/breezy/bzr/workingtree_4.py", line 245, in commit
result = WorkingTree.commit(self, message, revprops, *args,
File "/usr/lib/python3/dist-packages/breezy/mutabletree.py", line 172, in commit
committed_id = commit.Commit().commit(working_tree=self,
File "/usr/lib/python3/dist-packages/breezy/commit.py", line 446, in commit
self._process_post_hooks(old_revno, new_revno)
File "/usr/lib/python3/dist-packages/breezy/commit.py", line 612, in _process_post_hooks
self._process_hooks("post_commit", old_revno, new_revno)
File "/usr/lib/python3/dist-packages/breezy/commit.py", line 650, in _process_hooks
hook(hook_local, hook_master, old_revno, old_revid, new_revno,
File "/usr/lib/python3/dist-packages/breezy/plugins/email/__init__.py", line 83, in branch_commit_hook
emailer.EmailSender(master, new_revid, master.get_config_stack(),
File "/usr/lib/python3/dist-packages/breezy/plugins/email/emailer.py", line 266, in send_maybe
self.send()
File "/usr/lib/python3/dist-packages/breezy/plugins/email/emailer.py", line 210, in send
self._send_using_process()
File "/usr/lib/python3/dist-packages/breezy/plugins/email/emailer.py", line 218, in _send_using_process
diff = self.get_diff()
File "/usr/lib/python3/dist-packages/breezy/plugins/email/emailer.py", line 143, in get_diff
show_diff_trees(tree_old, tree_new, diff_content, None, diff_options)
File "/usr/lib/python3/dist-packages/breezy/diff.py", line 533, in show_diff_trees
return differ.show_diff(specific_files, extra_trees)
File "/usr/lib/python3/dist-packages/breezy/diff.py", line 1025, in show_diff
return self._show_diff(specific_files, extra_trees)
File "/usr/lib/python3/dist-packages/breezy/diff.py", line 1090, in _show_diff
self.to_file.write(b"=== modified %s '%s'%s\n" % (kind[0].encode('ascii'),
TypeError: string argument expected, got 'bytes'

brz 3.1.0 on python 3.9.1 (Linux-5.10.0-1-amd64-x86_64-with-glibc2.31)
arguments: ['/usr/bin/bzr', 'commit', '.', '-m', 'update parted to 3.4']
plugins: bash_completion[3.1.0], changelog_merge[3.1.0],
commitfromnews[3.1.0], cvs[3.1.0], darcs[3.1.0], email[3.1.0],
fastimport[3.1.0], flake8[unknown], fossil[3.1.0], github[3.1.0],
gitlab[3.1.0], hg[3.1.0], launchpad[3.1.0], mtn[3.1.0],
netrc_credential_store[3.1.0], news_merge[3.1.0], po_merge[3.1.0],
propose[3.1.0], quilt[unknown], repodebug[3.1.0], rewrite[unknown],
stats[3.1.0], svn[3.1.0], upload[3.1.0], weave_fmt[3.1.0],
zsh_completion[3.1.0]
encoding: 'ascii', fsenc: 'utf-8', lang: 'C'

*** Bazaar has encountered an internal error. This probably indicates a
bug in Bazaar. You can help us fix it by filing a bug report at
https://bugs.launchpad.net/brz/+filebug
including this traceback and a description of the problem.
make: *** [../../../gar/gar.mk:370: ci] Error 4