fast-export fails the simplest round-trip test

This is on Ubuntu 20, thus bzr 3.0.2-4ubuntu2

mkdir repo1.bzr
cd repo1.bzr
bzr init
echo "file" > file1
bzr add file1
bzr commit -m "add file1"
cd ..

bzr fast-export repo1.bzr - | bzr fast-import - repo1imported.bzr

Creating destination repository ...
17:32:39 Calculating the revisions to include ...
17:32:39 Starting export of 1 revisions ...
17:32:39 Exported 1 revision in 0:00:00
Shared repository with trees (format: 2a)
Location:
  shared repository: repo1imported.bzr
17:32:39 Starting import ...
brz: ERROR: TypeError: startswith first arg must be str or a tuple of str, not bytes

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/breezy/commands.py", line 1016, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/breezy/commands.py", line 1202, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python3/dist-packages/breezy/commands.py", line 759, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python3/dist-packages/breezy/commands.py", line 784, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/breezy/cleanup.py", line 136, in run_simple
    return _do_with_cleanups(
  File "/usr/lib/python3/dist-packages/breezy/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/breezy/plugins/fastimport/cmds.py", line 320, in run
    return _run(source, generic_processor.GenericProcessor,
  File "/usr/lib/python3/dist-packages/breezy/plugins/fastimport/cmds.py", line 51, in _run
    return proc.process(p.iter_commands)
  File "/usr/lib/python3/dist-packages/breezy/plugins/fastimport/processors/generic_processor.py", line 282, in process
    super(GenericProcessor, self)._process(command_iter)
  File "/usr/lib/python3/dist-packages/fastimport/processor.py", line 79, in _process
    for cmd in command_iter():
  File "/usr/lib/python3/dist-packages/fastimport/parser.py", line 298, in iter_commands
    elif len(line) == 0 or line.startswith(b'#'):
TypeError: startswith first arg must be str or a tuple of str, not bytes