[BUG][typescript-nextjs] Compilation error in generated *.service.ts file for multipart file upload

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?
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Description

When having multipart form data in schema, the generated api file has compilation error.
This is caused due a variable formParams only being initialized in if block and not in else block.

openapi-generator version

6.1.0, present in all versions

OpenAPI declaration file content or url

  /upload-file:
    post:
      tags:
        - File
      operationId: uploadFile
      summary: upload profile for user
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                file:
                  type: string
                  format: binary
      responses:
        '200':    # status code
          description: Success response
          content:
            application/json:
              schema: 
                type: string

Generation Details

npx @openapitools/openapi-generator-cli generate -i swagger.json -g typescript-nestjs -o temp

Caused by

https://github.com/OpenAPITools/openapi-generator/blob/c59759f20a18dd2aaba9586943d99987cfd76f12/modules/openapi-generator/src/main/resources/typescript-nestjs/api.service.mustache#L196

Since this line is commented out, typerscript compiler gives Variable 'formParams' is used before being assigned. for this.

Related issues/PRs

None

Suggest a fix

We can either

1. Throw an error in else block, this would calm the TS compiler.
2. Just uncomment the line and added necessary imports.
   (I don't have enough TypeScript context to understand its usage, but simple googling suggest its somehow related to angular so might not be required)

Start with modules/openapi-generator/src/main/resources/typescript-nestjs/api.service.mustache around line 196, then generate the provided multipart upload specification with the documented npx command. Inspect the generated api service and verify that TypeScript compilation no longer reports formParams as used before being assigned.