title: RxDart. Listener of BehaviorSubject does not get value after subject.add(value)
body: <p>I have two classes: CurrencyRepo and CurrencyFetcher. From CurrencyFetcher I try to listen to the behaviorSubject that is in the repo. But when I add values in the behaviorSubject inside the repo, CurrencyFetcher does not get these values. What am I doing wrong?</p>
  <pre><code>class CurrencyFetcher implements CurrencyFetcherService {
    final CurrencyRepo _currencyRepo;
    StreamSubscription currencySubscription;
  
    CurrencyFetcher(this._currencyRepo, this._preferencesService) {
      _subscribeToCurrencies();
    }
  
    void _subscribeToCurrencies() {
      currencySubscription = _currencyRepo
          .getCurrenciesStream()
          .listen((currencies) =&gt; _handleApiCurrencies);
    }
  
    Future&lt;void&gt; _handleApiCurrencies(List&lt;ApiCurrency&gt; apiCurrencies) async {
    // implemetation
    }
  }
  </code></pre>
  <pre><code>class CurrencyRepo {
    final CurrencyApi _currencyApi;
    final BehaviorSubject&lt;List&lt;ApiCurrency&gt;&gt; _currencySubject = BehaviorSubject.seeded([]);
  
    Stream&lt;List&lt;ApiCurrency&gt;&gt; getCurrenciesStream() {
      _updateCurrencies();
      return _currencySubject.stream;
    }
  
    CurrencyRepo(this._currencyApi);
  
    void _updateCurrencies() {
      _currencyApi.getCurrencies().then((currencies) {
        _currencySubject.add(currencies);
      });
    }
  }
  </code></pre>
  <p>I have checked that the values are added to the stream after the CurrencyFetcher starts to listen. And I have checked that in the moment, when I add new value to the stream, it has a listener. The first time using RxDart, may someone help? :)</p>