[BUG] Duplicated Interface created with typescript-axios and nullable option.

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

I have 1 type of object and I want to also use it as nullable: true. But adding the nullable: true option in an object create a new model instead of reusing the current one.

openapi-generator version

@openapitools/openapi-generator-cli 2.4.18

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: test
  version: local
paths:
  /test:
    get:
      responses:
        '200':
          content:
            application/json:
              schema:
                type: object
                title: ParentObject
                properties:
                  requiredChild:
                    type: object
                    title: ChildObject
                    properties:
                      name:
                        type: string
                  nullableChild:
                    type: object
                    title: ChildObject
                    properties:
                      name:
                        type: string
                    nullable: true

Generation Details

npx @openapitools/openapi-generator-cli@latest generate -i test.yaml -g typescript-axios -o ./test/

this will generate api.ts with the following model.

/**
 * 
 * @export
 * @interface ChildObject
 */
export interface ChildObject {
    /**
     * 
     * @type {string}
     * @memberof ChildObject
     */
    name?: string;
}
/**
 * 
 * @export
 * @interface ChildObject1
 */
export interface ChildObject1 {
    /**
     * 
     * @type {string}
     * @memberof ChildObject1
     */
    name?: string;
}
/**
 * 
 * @export
 * @interface ParentObject
 */
export interface ParentObject {
    /**
     * 
     * @type {ChildObject}
     * @memberof ParentObject
     */
    requiredChild?: ChildObject;
    /**
     * 
     * @type {ChildObject1}
     * @memberof ParentObject
     */
    nullableChild?: ChildObject1 | null;
}

Since the nullable field does not impact the interface of ChildObject, a new object name ChildObject1 should not be generated and both requiredChild and nullableChild should use the same interface.

Expected output:

/**
 * 
 * @export
 * @interface ChildObject
 */
export interface ChildObject {
    /**
     * 
     * @type {string}
     * @memberof ChildObject
     */
    name?: string;
}
/**
 * 
 * @export
 * @interface ParentObject
 */
export interface ParentObject {
    /**
     * 
     * @type {ChildObject}
     * @memberof ParentObject
     */
    requiredChild?: ChildObject;
    /**
     * 
     * @type {ChildObject1}
     * @memberof ParentObject
     */
    nullableChild?: ChildObject | null;
}

Start by running the reported command with the inline OpenAPI declaration in test.yaml and inspect the generated api.ts from the typescript-axios generator. Trace how the requiredChild and nullableChild schemas are named and compared. Done means both properties reference ChildObject while nullableChild retains its null type, without generating ChildObject1.