Set Headers using append or set does not work in Angular 2

问题

I am using Angular 2.4.8. I want to append custom headers to each request. I am using BaseRequestOptions to define custom headers and adding it to app providers. Following is the code.

import { BaseRequestOptions, Headers } from '@angular/http';
import { Injectable } from '@angular/core';

@Injectable()
export class AppBaseRequestOptions extends BaseRequestOptions {
  public merge(headers: Headers) {
    headers.append('Content-type', 'application/json');
    headers.append('My-Custom-Header', 'My-Custom-Header-Value');
    return super.merge(headers);
  }
}

Provider is as follows.

providers: [
    { provide: BaseRequestOptions, useClass: AppBaseRequestOptions }
  ]

I have tried headers.append and headers.set but both throws

Cannot read property 'append' of null
Cannot read property 'set' of null

回答1:

Did you forget?

let headers: Headers = new Headers();

来源：https://stackoverflow.com/questions/42555482/set-headers-using-append-or-set-does-not-work-in-angular-2