Angular 4 server-side autocomplete

test-material.component.html

<div class="container">
    <div class="row">
        <form class="example-form">
            <md-form-field class="example-full-width">
                <input type="text" mdInput [formControl]="myControl" [mdAutocomplete]="auto" placeholder="Health Topic Name">
                <md-autocomplete #auto="mdAutocomplete">
                    <md-option *ngFor="let option of serverOptions | async" [value]="option">
                        {{ option }}
                    </md-option>
                </md-autocomplete>
            </md-form-field>
        </form>
    </div>
</div>

test-material.component.ts

import { Component, OnInit } from '@angular/core';
import { FormControl } from '@angular/forms';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/startWith';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/debounce';
import 'rxjs/add/operator/delay';

import { SearchService } from './search.service';

@Component({
  selector: 'app-test-material',
  templateUrl: './test-material.component.html',
  styleUrls: ['./test-material.component.scss'],
  providers: [ SearchService ]
})
export class TestMaterialComponent implements OnInit {

  myControl: FormControl = new FormControl();

  options = [];

  serverOptions: Observable<string[]>;

  constructor(private searchService: SearchService) { }

  ngOnInit() {
    this.serverOptions = this.myControl.valueChanges
      .delay(new Date(Date.now() + 1000))
      .startWith(null)
      .map(val => val ? this.findTopics(val) : []);
  }

  findTopics(val) {
    this.searchService.autocomplete(val).then( results => {
      console.log(results);
      this.options = results;
      return results;
    });
  }
}

Maybe use the answers at https://stackoverflow.com/questions/43575515/md-autocomplete-angular2-getting-data-from-server-with-a-service

This doesn't work for me, I think that findTopics doesn't return any value, right?