[BUG][typescript-fetch] error TS2532: Object is possibly 'undefined' for optional model properties

[kota65535]

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

Given OpenAPI schema definition:

title: Task
description: Task
type: object
properties:
  id:
    type: integer
    readOnly: true
  title:
    type: string
  dueDate:
    type: string
    format: date
required:
  - id
  - title

Then generated source file Task.ts has a compilation error TS2532: Object is possibly undefined. The TypeScript version is 5.3.3 (latest).

openapi-generator version

At the current latest commit of the master branch (a8efb8e)

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Related issues/PRs

This bug seems to have been introduced by #17798.

Suggest a fix

Typescript compiler does not understand the function exists() ensures the value is present. exists() simply assert the value is not null or undefined, so a quick fix will be using == operator like this.

        'dueDate': value['dueDate'] == null  ? undefined : ((value['dueDate']).toISOString().substring(0,10)),

[wing328]

FYI @noordawod - the author of #17798

[topce]

Nice work @kota65535
Small remark
expression in

'dueDate': value['dueDate'] == null  ? undefined : ((value['dueDate']).toISOString().substring(0,10)), 

could be written in typescript

'dueDate': value.dueDate?.toISOString().substring(0,10)),

or

'dueDate': value['dueDate']?.toISOString().substring(0,10)),

so called optional chaining
could be future improvement
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#optional-chaining
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining