[BUG] [typescript-fetch] request body containing array of objects generates typescript not allowed in strict-mode

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

The code generated for an API POST-call having an array of objects as its body, is not valid if strict mode is enabled in typescript.

openapi-generator version

v6.4.0

OpenAPI declaration file content or url

https://gist.github.com/SimonSimCity/e3d86c8f4a0f16d0e329dbf2d593bf94

Generation Details

{
  "$schema": "./node_modules/@openapitools/openapi-generator-cli/config.schema.json",
  "spaces": 2,
  "generator-cli": {
    "version": "6.3.0",
    "generators": {
      "v2.0": {
        "generatorName": "typescript-fetch",
        "inputSpec": "./swagger.json",
        "output": "./generated/api"
      }
    }
  }
}

Steps to reproduce

Run the following commands in a directory containing the provided swagger.json file and the openapitools.json:

1. npx openapi-generator-cli generate
2. npx tsc --strict --target ESNext --moduleResolution node generated/api/index.ts

Related issues/PRs

--

Suggest a fix

The value of the property requestParameters.statisticsTrackPlayedPostRequestInner might be undefined, which could be solved by using optional chaining by adding a question mark before .map(. I just don't know whether this would still be compatible with the api specification or if the problem rather is that this actually can be undefined as of its definition ...

        const response = await this.request({
            path: `/Statistics/track/played`,
            method: 'POST',
            headers: headerParameters,
            query: queryParameters,
            body: requestParameters.statisticsTrackPlayedPostRequestInner.map(StatisticsTrackPlayedPostRequestInnerToJSON),
            //                                                           ^ Changing to "?.map(" might solve the issue already
        }, initOverrides);

Run the commands from the issue with swagger.json and openapitools.json, then inspect generated/api/index.ts and the typescript-fetch generator output around the request body mapping. Confirm the generated TypeScript fails under npx tsc --strict --target ESNext --moduleResolution node; done means the same generated client compiles successfully in strict mode.