Make typeddicts non-total.

Author: syastrov

mypy/plugins/dataclasses.py

@@ -464,7 +464,7 @@ def _asdictify_inner(typ: Type, seen_dataclasses: FrozenSet[str]) -> Type:
                     assert attr_type is not None
                     fields[attr.name] = _asdictify_inner(attr_type, seen_dataclasses)
                 return make_anonymous_typeddict(api, fields=fields,
-                                                required_keys=set(fields.keys()))
+                                                required_keys=set())
             elif info.has_base('builtins.list'):
                 supertype_instance = map_instance_to_supertype(typ, api.named_generic_type(
                     'builtins.list', []).type)