OpenAPI generator fails to type hint a file from NSwag

Question

I have a backend service written in .NET Core and I use NSwag to generate a Swagger client. My client app, which is written in TypeScript, uses this Swagger to generate code for the requests. This works perfectly fine except for files. I have one endpoint that downloads a file and this endpoint can't be automatically type-hinted no matter what! This is my code for the endpoint:

[HttpGet("{id}/download")]
[Produces("text/plain", Type = typeof(FileStreamResult))]
public ActionResult GenerateCreateTableStatements(long id)
{
    try
    {
        // code
        return new FileStreamResult(stream, "text/plain") { FileDownloadName = "text_file.txt" };

    }
    catch (Exception e)
    {
        return BadRequest(e.Message);
    }
}

This code produces the following configuration in the Swagger's json:

"/api/Project/{id}/download": {
  "get": {
    "tags": [
      "xx"
    ],
    "parameters": [
      {
        "name": "id",
        "in": "path",
        "required": true,
        "schema": {
          "type": "integer",
          "format": "int64"
        }
      }
    ],
    "responses": {
      "200": {
        "description": "Success",
        "content": {
          "text/plain": {
            "schema": {
              "type": "file"
            }
          }
        }
      }
    }
  }
}

Later on in my Typescript app, I run openapi-generator-cli generate -i URL/swagger/v1/swagger.json -g typescript-axios -o src/client and this generates me all of the code for all of the endpoints. For this particular endpoint that returns a FileStreamResult, I get

async apiProjectIdDownload(id: number, options?: AxiosRequestConfig): Promise<(axios?: AxiosInstance, basePath?: string) => AxiosPromise<any>> {
    const localVarAxiosArgs = await localVarAxiosParamCreator.apiProjectIdDownload(id options);
    return createRequestFunction(localVarAxiosArgs, globalAxios, BASE_PATH, configuration);
}

As you can see, it type-hints it as any instead of Blob which is my goal. I tried some suggestions from an open issue on NSwag's github but still no luck.

Has anyone stumbled upon an issue like this and how did you manage to resolve it?