ERROR TypeError: Cannot read property 'pipe' of null in NGRX Effect

Question

When I dispatching my action in my component this updateTour effect should be triggered. but this error appears in my browser console core.js:5847 ERROR TypeError: Cannot read property 'pipe' of null at SwitchMapSubscriber.project (updatetour.effects.ts:87) requestHandlerService.invoke(request).pipe causing the error. can someone explain what's wrong here

updataTour$ = createEffect(() =>
   this.actions$.pipe(
       ofType(TourproviderAction.updateTourprovider),
       switchMap((action) => {
       const data = action.tourProvider;
       const parameters: any = { tourProviderId: '1' };
       const queryParams = new HttpParams({
              fromObject: parameters
       })

        const options = {
                params: queryParams,
                headers: {
                    'Content-Type': 'application/json',
                    'Authorization': 'a5sfjdksfjksfe2f4af3673ce1a'
              }
         };

        const request = new ServiceRequest
       (environment.urls.tourProvider, 'POST', formData, options);
        return this.requestHandlerService.invoke(request).pipe(
                map((updateResponce) => {
             const responceData = JSON.stringify(updateResponce)
             return TourproviderAction.updateTourproviderSuccess({ responce: responceData });
                }),
                catchError(err => {
                    const errorMessage = JSON.stringify(err);
                    return of(TourproviderAction.updateTourproviderFail({ errorMessage }))
                })
            );
        })
    )
);

Answer 1

The error means that this line

this.requestHandlerService.invoke(request)

is returning null and cannot call pipe function. Make sure that you return Observable from invoke method so that you can pipe the reponses.