Mr.bob error when creating a new addon

I'm attempting to create a new addon using the instructions from the Plone Docs site on a Mac. I've created a new conda environment for Python 3.7, installed mr.bob 0.1.2 and bobtemplates.plone 5.1.1, and run mrbob -O plonetheme.tango bobtemplates:plone_addon, but I get this error:

Traceback (most recent call last):
  File "/Users/leaderone/miniconda3/envs/plone/bin/mrbob", line 8, in <module>
    sys.exit(main())
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/site-packages/mrbob/cli.py", line 155, in main
    defaults=defaults)
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/site-packages/mrbob/configurator.py", line 138, in __init__
    self.template_dir, self.is_tempdir = parse_template(template)
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/site-packages/mrbob/configurator.py", line 92, in parse_template
    path = resolve_dotted_path(template_name)
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/site-packages/mrbob/configurator.py", line 40, in resolve_dotted_path
    return os.path.join(os.path.dirname(module.__file__), dir_name)
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/posixpath.py", line 156, in dirname
    p = os.fspath(p)
TypeError: expected str, bytes or os.PathLike object, not NoneType

When I try creating an addon through plonecli, I get:

Traceback (most recent call last):
  File "/Users/leaderone/miniconda3/envs/plone/bin/mrbob", line 8, in <module>
    sys.exit(main())
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/site-packages/mrbob/cli.py", line 175, in main
    c.render()
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/site-packages/mrbob/configurator.py", line 199, in render
    f(self)
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/site-packages/bobtemplates/plone/addon.py", line 141, in post_render
    run_isort(configurator)
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/site-packages/bobtemplates/plone/utils.py", line 76, in run_isort
    cwd=root_folder,
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/subprocess.py", line 411, in check_output
    **kwargs).stdout
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/subprocess.py", line 488, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/subprocess.py", line 800, in __init__
    restore_signals, start_new_session)
  File "/Users/leaderone/miniconda3/envs/plone/lib/python3.7/subprocess.py", line 1551, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'tox': 'tox'

I also get errors using Python 2. What am I doing wrong?

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