Config check failed with add_subclass_arguments(required=False)

[carmocca]

from jsonargparse import ArgumentParser

class A:
    ...

class B:
    ...

parser = ArgumentParser()
parser.add_subclass_arguments((A, B), nested_key="foo", required=False)
args = parser.parse_args()

produces:

scratch_12.py: error: Configuration check failed :: Parser key "foo": Value {} does not validate against any of the types in typing.Union[__main__.A, __main__.B]:
  - Type <class '__main__.A'> expects an str or a Dict with a class_path entry but got "{}"
  - Type <class '__main__.B'> expects an str or a Dict with a class_path entry but got "{}"

My assumption was that by setting required=False, --foo does not need to be passed.
And args would be an empty dictionary.

[mauvilsa]

Fixed in v3.19.2

[carmocca]

@mauvilsa If I add the following line at the end of the snippet above, the error still appears:

args_init = parser.instantiate_classes(args)

Can you re-open this?

[carmocca]

Looking at the commit that closed this PR, I'd say that the assertion should be changed to self.assertEqual(cfg, {})