SVN module TypeError with Python 3.9

[PeterW-LWL]

Checking out a SVN repository fails with the following stack trace

mr.developer: Creating missing sources dir /project_path/src.
mr.developer: Queued 'source_name' for checkout.
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.9/threading.py", line 954, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.9/threading.py", line 892, in run
    self._target(*self._args, **self._kwargs)
  File "/project_path/eggs/mr.developer-2.0.1-py3.9.egg/mr/developer/common.py", line 170, in worker
    output = action(**kwargs)
  File "/project_path/eggs/mr.developer-2.0.1-py3.9.egg/mr/developer/svn.py", line 316, in checkout
    return self.svn_checkout(**kwargs)
  File "/project_path/eggs/mr.developer-2.0.1-py3.9.egg/mr/developer/svn.py", line 281, in svn_checkout
    return self._svn_error_wrapper(self._svn_checkout, **kwargs)
  File "/project_path/eggs/mr.developer-2.0.1-py3.9.egg/mr/developer/svn.py", line 123, in _svn_error_wrapper
    return f(**kwargs)
  File "/project_path/eggs/mr.developer-2.0.1-py3.9.egg/mr/developer/svn.py", line 177, in _svn_checkout
    stdout, stderr, returncode = self._svn_communicate(args, url, **kwargs)
  File "/project_path/eggs/mr.developer-2.0.1-py3.9.egg/mr/developer/svn.py", line 207, in _svn_communicate
    if 'authorization failed' in lines[-1] or 'Could not authenticate to server' in lines[-1]:
TypeError: a bytes-like object is required, not 'str'

mr.developer 2.0.1
zc.buildout 2.13.7
svn 1.14.1
Python 3.9.2