xml file loading showing json error

in my app i am trying to load XML file in order to use his data. but i am facing an error in Chrome browser console:

{error: SyntaxError: Unexpected token < in JSON at position 0 at JSON.parse () at XMLHttp…,

service.ts

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';

@Injectable()
export class ReadDataService {
  headers = new HttpHeaders({ 'Content-Type': 'text/xml' });
  xml: string;
  private _url: string = "../../assets/sf9_commandpacket.xml";

 constructor(private _http:HttpClient) {}

  getData(): Observable<string> {
  return this._http.get<string>(this._url, { headers: this.headers });
  }
 }
}

i see in the error, that he is trying to load json, why?

I tried to implement this solution:

this._http.get(this._url, { headers: this.headers, responseType: text / xml }).subscribe(response => { return response; })

but this appear:

also tried to surrong with ':