title: Type 'void' is not assignable to type 'ObservableInput<any>'
body: <p>I am getting the following error</p>
  
  <blockquote>
    <p>Argument of type '(user: User) => void' is not assignable to parameter
    of type '(value: User, index: number) => ObservableInput'. Type
    'void' is not assignable to type 'ObservableInput'.</p>
  </blockquote>
  
  <pre><code> getCurrentUserDb()
    {
      return this.login.authState.pipe(
                          switchMap(user=&gt;{
                            return this.serviceUsers.getUserByuid(user.uid);
                          }),
                          map(user=&gt;{
                            return user;
                          })
      )
    }
  </code></pre>