title: Why would it give JSON.stringfy error, even when I have not used it?
body: <p>I am building application in nodejs where I have to display the data by hitting the HTTPS endpoint. I am using Swagger UI to display the data. I am getting following error </p>
  
  <pre><code>Converting circular structure to JSON +1169ms
  TypeError: Converting circular structure to JSON
      at JSON.stringify (&lt;anonymous&gt;)
      at stringify (node_modules/express/lib/response.js:1123:12)
      at ServerResponse.json (node_modules/express/lib/response.js:260:14)
      at ExpressAdapter.reply (node_modules/@nestjs/platform-express/adapters/express-adapter.js:23:57)
      at RouterResponseController.apply (node_modules/@nestjs/core/router/router-response-controller.js:10:36)
      at @nestjs/core/router/router-execution-context.js:163:48
      at process._tickCallback (internal/process/next_tick.js:68:7)
  </code></pre>
  
  <p>even when I have <code>not used JSON.stringfy</code> in my code. How can I resolve this error?
  Here is my controller.ts code</p>
  
  <pre><code>import { Observable } from 'rxjs';
  
  @Controller('/service/api/message')
  export class MessageController {
  
    source: string;
    productCode: string;
    vehicleType: string;
    constructor(private messageService: MessageService) {}
  @Post()
    @ApiUseTags('processor-dispatcher')
    @ApiOperation({ title: 'Generate product message for the SNS topics' })
    async generateMessage(@Body() productEvent: ProductEvent) {
  
      return this.messageService
        .getData(this.source, this.productCode, this.vehicleType)
        .subscribe(res =&gt; {
          console.log(res);
        });
    }
  }
  
  </code></pre>
  
  <p>Here is my service.ts</p>
  
  <pre><code>import Axios, { AxiosResponse } from 'axios';
  
  @Injectable()
  export class MessageService {
    constructor(private readonly httpService: HttpService) {}
  
    configEndPoint: string =
      'https:www.xyz.com';
  
  
    getData(
      source: string,
      productCode: string,
      vehicleType: string,
    ): Observable&lt;any&gt; {
      return this.httpService.get(this.configEndPoint, { validateStatus: null });
  
    }
  }
  
  </code></pre>