Fails to parse list parameter from cli argument: JSONDecodeError

[ymentha14]

foo.py

import luigi

class Foo(luigi.Task):
    bar = luigi.ListParameter(default="['foo']")
    def run(self):
        print(f"Running task {self}")
    def output(self):
        return luigi.LocalTarget("./foo.txt")

Running luigi --module foo Foo --bar 'bar' results in json.decoder.JSONDEcodeError: Expecting value: line1 column 1 (char 0)

Stacktrace:

ERROR: Uncaught exception in luigi
Traceback (most recent call last):
  File "/home/lib/python3.8/site-packages/luigi/retcodes.py", line 75, in run_with_retcodes
    worker = luigi.interface._run(argv).worker
  File "/home/lib/python3.8/site-packages/luigi/interface.py", line 213, in _run
    return _schedule_and_run([cp.get_task_obj()], worker_scheduler_factory)
  File "/home/lib/python3.8/site-packages/luigi/cmdline_parser.py", line 114, in get_task_obj
    return self._get_task_cls()(**self._get_task_kwargs())
  File "/home/lib/python3.8/site-packages/luigi/cmdline_parser.py", line 131, in _get_task_kwargs
    res.update(((param_name, param_obj.parse(attr)),))
  File "/home/lib/python3.8/site-packages/luigi/parameter.py", line 1140, in parse
    i = json.loads(x, object_pairs_hook=FrozenOrderedDict)
  File "/usr/lib/python3.8/json/__init__.py", line 370, in loads
    return cls(**kw).decode(s)
  File "/usr/lib/python3.8/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.8/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Expected Behavior:
The command should complete successfully

OS: Ubuntu
python: 3.8.10
luigi : 3.1.1

[lallea]

According to the docs, ListParameter accepts a JSON format list, e.g. `--bar '["bar"]'`. https://luigi.readthedocs.io/en/stable/api/luigi.parameter.html#luigi.parameter.ListParameter