[BUG][typescript-angular] Configuration template generates code that fails strict type checking

[Toeler]

Description

The code generated by the typescript-angular template results in code that fails the strictNullChecks compiler option for Typescript

openapi-generator version

5.0.1 - issue added in 5.0.0 via #6953

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  version: '1.0'
  title: Example API
paths:
  /securitySchemeA:
    get:
      responses:
        default:
          description: successful operation
components:
  securitySchemes:
    ExampleA:
      type: apiKey
      name: Authorization
      in: header

Command line used for generation

openapi-generator generate -g typescript-angular -i openapi.yml

Steps to reproduce

Use the spec file and command provided above to generate a client.
Then run the command npx tsc configuration.ts --lib esnext --strictNullChecks.
Ignore the error Cannot find module '@angular/common/http'.
Observe two errors stating Object is possibly 'undefined'

Related issues/PRs

Not that I can see

Suggest a fix/enhancement

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/typescript-angular/configuration.mustache#L67
The code could be changed to use Optional Chaining (?.) to access the keys on this.apiKeys, since apiKeys is nullable. e.g. this.apiKeys?.['{{name}}']
Alternatively, it could simply check for the truthiness of apiKeys before accessing it.

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