title: ngrx effects gives Type 'void' is not assignable to type 'ObservableInput'
body: <pre><code>@Injectable()
  export class ApiSearchEffects {
  
    @Effect()
    search$: Observable&lt;any&gt;
      = this.actions$
      .ofType(query.ActionTypes.QUERYSERVER)
      .debounceTime(300)
      .map((action: query.QueryServerAction) =&gt; action.payload)
      .switchMap(payload =&gt; {
        console.log(payload);
        const nextSearch$ = this.actions$.ofType(query.ActionTypes.QUERYSERVER).skip(1);
  
        this.searchService.getsearchresults(payload)
          .takeUntil(nextSearch$)
          .map((response) =&gt;
            ({type: '[Search] Change', payload: response}
            ))
      });
  </code></pre>
  
  <p>above code gives me Argument of type '(payload: any) => void' is not assignable to parameter of type '(value: any, index: number) => ObservableInput'.
    Type 'void' is not assignable to type 'ObservableInput'. 
  where could be the mistake be. I have followed the ngrx effects official intro at <a href="https://github.com/ngrx/effects/blob/master/docs/intro.md" rel="nofollow noreferrer">https://github.com/ngrx/effects/blob/master/docs/intro.md</a> .</p>