Nest - UndefinedInterceptor

undefined.interceptor.ts

import { CallHandler, ExecutionContext, Injectable, NestInterceptor } from '@nestjs/common';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';

@Injectable()
export class UndefinedInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    return next
      .handle()
      .pipe(map(value => this.traverse(value)));
  }

  traverse(data: any) {
    for (const key in data) {
      if (typeof data[key] === 'undefined') {
        data[key] = null;
      }
      if (data[key] !== null && typeof(data[key]) === 'object') {
        this.traverse(data[key]);
      }
    }
    return data;
  }
}

Add this line to main.ts file

app.useGlobalInterceptors(new UndefinedInterceptor());