[BUG][aspnetcore] incorrect nullable type generated from default nullable config and DateTimeOffset config

Created by: yilinjuang

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

1. Without nullable (default should be false)

Model is still nullable.

        [DataMember(Name="bar", EmitDefaultValue=false)]
        public bool? Bar { get; set; }

2. nullable: false with config "useDateTimeOffset": true

Model is still nullable.

        [DataMember(Name="bar", EmitDefaultValue=false)]
        public DateTimeOffset? Bar { get; set; }

openapi-generator version

4.1.0

OpenAPI declaration file content or url

1. Without nullable (default should be false)

openapi: 3.0.2
info:
  title: Test
  version: 0.1.0
servers:
  - url: http://localhost
paths:
  /:
    get:
      operationId: test
      responses:
        200:
          description: test
components:
  schemas:
    Foo:
      type: object
      properties:
        bar:
          type: boolean

2. nullable: false with config "useDateTimeOffset": true

openapi: 3.0.2
info:
  title: Test
  version: 0.1.0
servers:
  - url: http://localhost
paths:
  /:
    get:
      operationId: test
      responses:
        200:
          description: test
components:
  schemas:
    Foo:
      type: object
      properties:
        bar:
          type: string
          format: date-time
          nullable: false

Command line used for generation

1. openapi-generator generate -i test.yaml -g aspnetcore -o test
2. openapi-generator generate -i test.yaml -g aspnetcore -o test -c config.json

config.json

{
  "useDateTimeOffset": true
}

Steps to reproduce

Generate and check the model file.

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/2269

Suggest a fix