how to inject a service in Ember App with Typescript

I am following this guide: https://v4.chriskrycho.com/2018/typing-your-ember-update-part-1.html

Here I have a service, which only have one function findAllContacts:

export default class ContactPicker extends Service {
  findAllContacts(): Promise<Contact[]> {
    return Promise.resolve(getContact());
  }
}

declare module '@ember/service' {
  interface Registry {
    'contact-picker': ContactPicker;
  }
}

and a phonebook component:

import Component from '@ember/component';
import Computed from "@ember/object/computed";
import ContactPicker from '../services/contact-picker';
import { inject as service } from '@ember/service';
export default class PhonebookView extends Component {
  contactPicker: Computed<ContactPicker> = service('contact-picker');

  didInsertElement() {
    let contacts = this.contactPicker.findAllContacts(); //error
  }
};

but I got typescript error when call this.contactPicker.findAllContacts(): Property 'findAllContacts' does not exist on type 'ComputedProperty'.ts(2339)

how to inject service with Typescript?