Angular – Error TS2355: A function whose declared type is neither ‘void’ nor ‘any’ must return a value

I'm using an auth guard in angular 5 to check if the user should be able to navigate to a specific page. I am getting an error related to returning an observable:

A function whose declared type is neither 'void' nor 'any' must return a value.

This is my authguard.ts

import { Injectable } from '@angular/core';
import { Router, CanActivate, ActivatedRoute, ActivatedRouteSnapshot, RouterStateSnapshot } from '@angular/router';
import { ApplicationVerificationService } from '../../service/application-verification.service';

@Injectable() export class AppStatusGuard implements CanActivate {

  applicationId: number;   personId: number;

  constructor(
    public router: Router,
    public readonly activeRoute: ActivatedRoute,
    public readonly applicationVerificationService: ApplicationVerificationService) { }

  loginRoute: boolean;   memberRoute: boolean;


  canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): boolean {

    this.applicationId = Number(route.params["applicationId"]);
    this.personId = Number(route.params["personId"]);

    // Make sure they are allowed on this page, if not re-direct
    const url = this.applicationVerificationService.getRouteForFellowshipApplicant(this.personId, this.applicationId)
      .subscribe((res: string) => {
        console.log(url);

        if (res !== `application-status/${this.personId}/${this.applicationId}`) {
          console.log("failure");
          // this.router.navigateByUrl(url);
          return false;
        } else {
          console.log("success");
          //this.router.navigateByUrl(url);
          return true;
        }
      });   
  }; 
};

This is my verification service

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Router } from '@angular/router';
import 'rxjs/Rx';
import { Observable } from 'rxjs/Observable';

@Injectable()
export class ApplicationVerificationService {
  constructor(
    private readonly httpClient: HttpClient,
    private readonly router: Router) { }

  getRouteForFellowshipApplicant(personId, applicationId): Observable<string> {
    this.httpClient.get('api/application-verification/' + personId).subscribe((responseObject: IFellowshipApplicationStatus) => {

      return Observable.create(observer => {

        if (responseObject.preApplicationVerificationStatus === 'GoToTrackerPage') {
          observer.next('application-status/' + personId + '/' + applicationId);
        }
        if (responseObject.preApplicationVerificationStatus === 'GoToApplicationFormPage') {
          observer.next('application-form/' + personId + '/' + applicationId);
        }
        if (responseObject.preApplicationVerificationStatus === 'GoToContactIceForInfoPage') {
          observer.next('contact-us/' + personId + '/' + applicationId);
        }
        if (responseObject.preApplicationVerificationStatus === 'GenericError') {
          observer.next('application-error/' + personId);
        }
        observer.complete();
      });
    });
    return null;
  }
}

I'm new to rxjs and I think I've made an error with how I am returning observable but I'm struggling a bit. Any help would be appreciated.