TypeError occurs when creating a harvest_source.

[dassolkim]

I am using ckan versions 2.9.5.
I tried to create a harvest_source in the UI (localhost:5000/harvest), but the error below occurred.

2022-03-10 15:32:01,615 ERROR [ckan.config.middleware.flask_app] str cannot be used as validator because it is not a user-defined function
Traceback (most recent call last):
  File "/home/dskim/ckan/lib/default/src/ckan/ckan/lib/navl/dictization_functions.py", line 246, in convert
    nargs = converter.__code__.co_argcount
AttributeError: type object 'str' has no attribute '__code__'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/ckan/default/lib/python3.8/site-packages/flask/app.py", line 1516, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/lib/ckan/default/lib/python3.8/site-packages/flask/app.py", line 1502, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
  File "/usr/lib/ckan/default/lib/python3.8/site-packages/flask/views.py", line 84, in view
    return current_app.ensure_sync(self.dispatch_request)(*args, **kwargs)
  File "/usr/lib/ckan/default/lib/python3.8/site-packages/flask/views.py", line 158, in dispatch_request
    return current_app.ensure_sync(meth)(*args, **kwargs)
  File "/home/dskim/ckan/lib/default/src/ckan/ckan/config/middleware/../../views/dataset.py", line 615, in post
    pkg_dict = get_action(u'package_create')(context, data_dict)
  File "/home/dskim/ckan/lib/default/src/ckan/ckan/logic/__init__.py", line 523, in wrapped
    result = _action(context, data_dict, **kw)
  File "/home/dskim/ckan/lib/default/src/ckan/ckan/logic/action/create.py", line 180, in package_create
    data, errors = lib_plugins.plugin_validate(
  File "/home/dskim/ckan/lib/default/src/ckan/ckan/lib/plugins.py", line 328, in plugin_validate
    return validate(data_dict, schema, context)
  File "/home/dskim/ckan/lib/default/src/ckan/ckan/lib/navl/dictization_functions.py", line 307, in validate
    flat_data, errors = _validate(flattened, schema, validators_context)
  File "/home/dskim/ckan/lib/default/src/ckan/ckan/lib/navl/dictization_functions.py", line 360, in _validate
    convert(converter, key, converted_data, errors, context)
  File "/home/dskim/ckan/lib/default/src/ckan/ckan/lib/navl/dictization_functions.py", line 250, in convert
    raise TypeError(
TypeError: str cannot be used as validator because it is not a user-defined function

[SeffatChowdhury]

I can report the same behavior with CKAN v2.9 running on docker