schema().dumps not working properly with field initializers

[ropottnik]

Consider the following dataclass:

from typing import List

from dataclasses import dataclass, field
from dataclasses_json import dataclass_json

@dataclass_json
@dataclass
class Bar:
    foos: List[str] = field(default_factory=list)

using Bar.schema().dumps(Bar()) gives me the following error:

Traceback (most recent call last):
  File "dataclass_test.py", line 20, in <module>
    Bar.schema().dumps(Bar())
  File "~/.venv/venv/lib/python3.6/site-packages/dataclasses_json/api.py", line 100, in schema
    infer_missing)
  File "~/.venv/venv/lib/python3.6/site-packages/dataclasses_json/mm.py", line 90, in _make_default_fields
    cls)
  File "~/.venv/venv/lib/python3.6/site-packages/dataclasses_json/mm.py", line 105, in _make_default_field
    type_arg = type_.___args__[0]
AttributeError: type object 'List' has no attribute '___args__'

Process finished with exit code 1

However, it works when the type of foos is a List of another dataclass_json, like this:

@dataclass_json
@dataclass
class Foo:
    one: str


@dataclass_json
@dataclass
class Bar:
    foos: List[Foo] = field(default_factory=list)


if __name__ == "__main__":
    print(Bar.schema().dumps(Bar()))

So something seems to be off with types and field initializers

I am using dataclasses-json==0.2.1

[ghost]

I've also just hit upon the exact same issue.