ValueError: unconverted data remains: -01

[vorburger]

I have installed this as per #64, and used bean-example >example.beancount, and then added this to example.beancount as per the README:

2000-01-01 custom "fava-extension" "fava_envelope" "{}"
2010-01-01 custom "envelope" "start date" "2020-01-01"
2020-01-01 custom "envelope" "budget account" "Assets:Checking"

but when starting fava example.beancount the follow error occurred when clicking on "Envelope Budget":

Exception on /example-beancount-file/extension/EnvelopeBudget/ [GET]
Traceback (most recent call last):
  File "/home/vorburger/.local/lib/python3.11/site-packages/flask/app.py", line 2525, in wsgi_app
    response = self.full_dispatch_request()
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vorburger/.local/lib/python3.11/site-packages/flask/app.py", line 1822, in full_dispatch_request
    rv = self.handle_user_exception(e)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vorburger/.local/lib/python3.11/site-packages/flask/app.py", line 1820, in full_dispatch_request
    rv = self.dispatch_request()
         ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vorburger/.local/lib/python3.11/site-packages/flask/app.py", line 1796, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vorburger/.local/lib/python3.11/site-packages/fava/application.py", line 360, in extension_report
    content = Markup(render_template_string(template, extension=extension))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vorburger/.local/lib/python3.11/site-packages/flask/templating.py", line 159, in render_template_string
    return _render(app, template, context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vorburger/.local/lib/python3.11/site-packages/flask/templating.py", line 130, in _render
    rv = template.render(context)
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vorburger/.local/lib/python3.11/site-packages/jinja2/environment.py", line 1301, in render
    self.environment.handle_exception()
  File "/home/vorburger/.local/lib/python3.11/site-packages/jinja2/environment.py", line 936, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "<template>", line 11, in top-level template code
  File "/home/vorburger/.local/lib/python3.11/site-packages/fava_envelope/__init__.py", line 30, in get_budgets_months_available
    self.generate_budget_df(currency)
  File "/home/vorburger/.local/lib/python3.11/site-packages/fava_envelope/__init__.py", line 20, in generate_budget_df
    module = BeancountEnvelope(
             ^^^^^^^^^^^^^^^^^^
  File "/home/vorburger/.local/lib/python3.11/site-packages/fava_envelope/modules/beancount_envelope.py", line 54, in __init__
    self.date_start = datetime.datetime.strptime(
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.11/_strptime.py", line 568, in _strptime_datetime
    tt, fraction, gmtoff_fraction = _strptime(data_string, format)
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.11/_strptime.py", line 352, in _strptime
    raise ValueError("unconverted data remains: %s" %
ValueError: unconverted data remains: -01