How to correctly return a void Observable?

Question

In my Angular 4 application, I have a method that have to return an Observable. This method has 3 conditions. First and second conditions make a get call, but the third condition does nothing and in this case I have to return an Observable as well, because this method is the first part of a .flatmap operator. So to chain the second part of the .flatmap operator, I need an Observable from the first part.

I've tried return new Observable<void>();, but I've got an error:

ERROR TypeError: Cannot read property 'subscribe' of undefined

This is the initial method that calls a service to load the data.

loadModelData() {       this.customerService.getModelDetail(this.code)         .subscribe(response => {           this.selected = response.body as Customer;         });     }   } 

This is the service method that have to chain 2 calls.

getModelDetail(code) {      const params = new HttpParams().set('projection', 'withBalance');      return this.endPointUrlService.loadMaps(this.entityLink)        .flatMap((res) => {         return this.http.get(this.endPointUrlService.cutLinks(           this.endPointUrlService.map.get('customers')) + '/' + code, {observe: 'response', params: params})           .map((response) => <any>response);       })   } 

And this is the methods from a support service. checkIfMapIsReady() is a method that returns a void Observable in the third case:

  loadMaps(entityLink: EntityLink[]): Observable<void> {     console.log(entityLink);      for (const i in entityLink) {       if (entityLink.hasOwnProperty(i)) {       return this.checkIfMapIsReady(entityLink[i].name, entityLink[i].searchMap, entityLink[i].endPoints[0])       }     }   }     public checkIfMapIsReady(modelName: string, mapName: string, endPoints: string) {      if (this.map.get(modelName) === undefined) {       console.log('endpoint url service All maps undefined ' + modelName);       return this.getLinks(modelName, this.mapNames.get(mapName), false)     } else {       console.log('endpoint url service Populate only ' + mapName);       if (this.mapNames.get(mapName).get(endPoints) === undefined) {       return  this.getLinks(modelName, this.mapNames.get(mapName), true)       } else {         return new Observable<void>();       }     }   } 

Answer 1

return of(); doesn't create a stream.

Whereas

return of(void 0);

does.

if you are mocking and need to return a stream of void. Like my life. [Sad Panda]