Optional not generated for nullable strings in OpenAPI

Describe the bug

When using type: string in combination with nullable: true in an OpenAPI specification, the resulting type should be Optional[str] but it is not.

To Reproduce

Example schema:

openapi: 3.0.3
info:
  version: 1.0.0
  title: testapi
  license:
    name: proprietary
servers: []
paths: {}
components:
  schemas:
    TopLevel:
      type: object
      properties:
        cursors:
          type: object
          properties:
            prev:
              type: string
              nullable: true
          required:
          - prev
      required:
      - cursors

Used commandline:

$ env/bin/datamodel-codegen --input spec.yaml --output test.py

Expected behavior

The generated class should be

class Cursors(BaseModel):
    prev: Optional[str]

but currently it is:

class Cursors(BaseModel):
    prev: str

Version:

• OS: Linux
• Python version: 3.9
• datamodel-code-generator version: 0.7.0

[languitar]

Thank you again for being so quick on this one! This looks now exactly as expected!

[goodoldneon]

Thank you so much for the quick fix, @koxudaxi! The new version fixes my problem when I use the --strict-nullable flag. I really appreciate your responsiveness, and thanks for maintaining such a great tool!