title: Conditionally return actions in NgRx effect
body: <p>I'm trying to check a condition in the effect and dispatch different actions based on the condition result. The conditional parameters are obtained from Store and a API call like below.</p>
  
  <pre><code>@Effect()
  // error here - Observable&lt;void&gt; is not assignable to type Observable&lt;Action&gt;
    loadUserSkills$: Observable&lt;Action&gt; = this.actions$
      .ofType(UserActionTypes.REQUEST_USER_SKILLS)
      .withLatestFrom(this.store$)
      .map(([action, storeState]) =&gt; {
        this.skillsService.getUserSkillsCacheVersion().
          map((cacheVersion) =&gt; {
            if (cacheVersion === storeState.users.cacheVersion.userSkills) {
              return new UsersActions.RequestUserSkillsFromStore();
            } else {
              return new UsersActions.RequestUserSkillsFromServer();
            }
          });
        });
  </code></pre>
  
  <p>What's not correct here?</p>