Incorrect parsing of null as nullable enum value serialized as strings

Consider the following schema definition (which passes validation with the openapitools/openapi-generator-cli container image):

// [...]
          "deviceEncryptionKeyScheme": {
            "$ref": "#/components/schemas/DeviceEncryptionKeyScheme",
            "nullable": true  // <-- nullability declared
          },

// [...]
      "DeviceEncryptionKeyScheme": {
        "enum": ["Default8"],
        "type": "string"
      },

It looks as if openapi-python-client version 0.23.1 supports deserialization with the deviceEncryptionKeyScheme property being unset, but not it being null:

        _device_encryption_key_scheme = d.pop("deviceEncryptionKeyScheme", UNSET)
        device_encryption_key_scheme: Union[Unset, DeviceEncryptionKeyScheme]
        if isinstance(_device_encryption_key_scheme, Unset):
            device_encryption_key_scheme = UNSET
        else:
            device_encryption_key_scheme = DeviceEncryptionKeyScheme(_device_encryption_key_scheme)

This looks like a bug to me.

使用 openapi-python-client 0.23.1 的行為和所示的產生反序列化程式碼，重現 issue 中的 nullable enum 情況。從 d.pop 之後對 deviceEncryptionKeyScheme 的處理開始；比較 UNSET 路徑與 null 路徑。當明確設為 null 的值能成功反序列化，而未設定的屬性仍表示為 UNSET 時，即表示完成。