codegen for nullable Enum throws AttributeError

Hi,

we have encountered a problem when trying to generate code for nullable Enums. This bug is present since at least version 0.7.3.

Describe the bug When generating code from an OpenAPI 3.0.3 spec with a nullable enum for my python project, the datamodel-codegen throws an AttributeError 'NoneType'" object has no attribute 'isIdentifier' though it should be possible to model nullable enums:

https://swagger.io/docs/specification/data-models/enums/

To Reproduce

Example schema v1.yaml:

openapi: 3.0.3
info:
  version: 0.1.1
  title: testing-enums
paths:
  /product/{product_id}/security-class:
    get:
      description: get the securityClass of a product
      parameters:
      - in: path
        name: product_id
        required: true
        schema:
          type: str
      responses:
        '200':
          description: A Uuid that corresponds to a running task
            content:
              application/json:
                schema:
                  $ref: '#/components/schemas/SecurityClass'
components:
  schemas:
    SecurityClass:
      type: string
      nullable: true
      enum:
      - RC1
      - RC1N
      - RC2
      - RC2N
      - RC3
      - RC4
      - null

Used commandline:

$ datamodel-codegen --disable-timestamp --use-default --strict-nullable --input ~/v1.yaml --output ~/my-project/models/scheduler_v1.py'

Expected behavior The models are generated correctly something like:

class SecurityClass:
   __root__: Optional[SecurityClassEnum] = None

class SecurityClassEnum(Enum):
    RC1 = "RC1"
    RC1N = "RC1N"
    RC2 = "RC2"
    RC2N = "RC2N"
    RC3 = "RC3"
    RC4 = "RC4"

Version:

• OS: Ubuntu x64 20.04
• Python version: 3.9
• datamodel-code-generator version: 0.8.1

Additional context Add any other context about the problem here.

[koxudaxi]

@mybr4inhurts I relased a new version as 0.8.2 The problem is fixed on the version.

[koxudaxi]

@mybr4inhurts

Also the codegen would create different models for either with or without the null element.

Yes, I expect this behavior. I don’t want to break current behavior because this code-generator is used in a lot of projects.

I implemented nullable-enum only for nullable == true and type == string. The previous version of the generator couldn’t generate a valid Enum class with the pattern. (You said the problem on the head of this issue.) It means we didn’t break the behavior and fixed it.

But, I agree with your suggestion. The generator should tell about invalid OpenAPI Schema to users. What do you think to show a warning message when nullable is true when null is no in the enum?