TypeError: __str__ returned non-string (type CVSDirFormat)

This happens when you do "brz log" in a directory which is not a breezy/bazaar repository, but happens to be a CVS checkout. A nicer error message would be good.

$ brz log
Traceback (most recent call last):
  File "/usr/pkg/lib/python3.9/site-packages/breezy/commands.py", line 1017, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/commands.py", line 1206, in run_bzr
    ret = run(*run_argv)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/commands.py", line 757, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/commands.py", line 782, in run
    return class_run(*args, **kwargs)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/commands.py", line 1223, in ignore_pipe
    result = func(*args, **kwargs)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/builtins.py", line 2853, in run
    dir, relpath = controldir.ControlDir.open_containing(location)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/controldir.py", line 771, in open_containing
    return klass.open_containing_from_transport(transport)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/controldir.py", line 792, in open_containing_from_transport
    result = klass.open_from_transport(a_transport, probers=probers)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/controldir.py", line 759, in open_from_transport
    format.check_support_status(_unsupported)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/plugins/cvs/__init__.py", line 58, in check_support_status
    raise CVSUnsupportedError(self)
breezy.plugins.cvs.CVSUnsupportedError: <exception str() failed>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/pkg/bin/brz", line 75, in <module>
    main()
  File "/usr/pkg/lib/python3.9/site-packages/breezy/__main__.py", line 59, in main
    exit_val = breezy.commands.main()
  File "/usr/pkg/lib/python3.9/site-packages/breezy/commands.py", line 1288, in main
    ret = run_bzr_catch_errors(argv)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/commands.py", line 1302, in run_bzr_catch_errors
    return exception_to_return_code(run_bzr, argv)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/commands.py", line 1022, in exception_to_return_code
    exitcode = trace.report_exception(exc_info, sys.stderr)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/trace.py", line 510, in report_exception
    report_user_error(exc_info, err_file)
  File "/usr/pkg/lib/python3.9/site-packages/breezy/trace.py", line 543, in report_user_error
    err_file.write(("brz: ERROR: %s\n" % (str(exc_info[1]),)))
TypeError: __str__ returned non-string (type CVSDirFormat)