[REQ][Python] Remove Optional[] from from_dict/from_json method in models

[unarist]

Is your feature request related to a problem? Please describe.

This generated from_dict method returns None only if None is passed as obj.

openapi-generator/samples/client/echo_api/python/openapi_client/models/pet.py

Lines 101 to 118 in c96d308

	@classmethod
	def from_dict(cls, obj: Optional[Dict[str, Any]]) -> Optional[Self]:
	"""Create an instance of Pet from a dict"""
	if obj is None:
	return None
	if not isinstance(obj, dict):
	return cls.model_validate(obj)
	_obj = cls.model_validate({
	"id": obj.get("id"),
	"name": obj.get("name"),
	"category": Category.from_dict(obj["category"]) if obj.get("category") is not None else None,
	"photoUrls": obj.get("photoUrls"),
	"tags": [Tag.from_dict(_item) for _item in obj["tags"]] if obj.get("tags") is not None else None,
	"status": obj.get("status")
	})
	return _obj

So I need to check its return value every time even if I actually passing non-None value...

pet = Pet.from_dict(pet_dict)
assert(pet is not None)

# or

if pet is None:
  raise Exception("should not be reached here")

Describe the solution you'd like

Remove Optional[] from the obj parameter and the return value.

 def from_dict(cls, obj: Dict[str, Any]) -> Self: 
     """Create an instance of Pet from a dict""" 
     if not isinstance(obj, dict): 
         return cls.model_validate(obj) 

    ...

Describe alternatives you've considered

@overload also provides better typing:

    @overload
    def from_dict(cls, obj: None) -> None:
        ...

    @overload
    def from_dict(cls, obj: Dict[str, Any]) -> Self:
        ...

    @classmethod
    def from_dict(cls, obj: Optional[Dict[str, Any]]) -> Optional[Self]:
        """Create an instance of Pet from a dict"""
        if obj is None:
            return None

        ...

but I don't think this method should accept None value. I'm agree with checking None in caller side, like the commit which introduce None checking does.

Additional context