title: how to check if Observable is empty or returns Boolean value
body: <p>lets say i have observable that call rest api service then store the result in database: </p>
  
  <pre class="lang-java prettyprint-override"><code>public Observable&lt;Boolean&gt; initDB() {
      return this.restApi.feedsEntityList()
          .flatMap(feedEntityList -&gt; this.mNewsCache.saveFeeds(feedEntityList));
  }
  </code></pre>
  
  <p>the save Observable perform the database saving and should return true in case of success or false in case of an error occurred:</p>
  
  <pre class="lang-java prettyprint-override"><code>public Observable&lt;Boolean&gt; saveFeeds(List&lt;FeedEntity&gt; feedEntity) {
     if (feedEntity != null) {
         return Observable.create(new Observable.OnSubscribe&lt;Boolean&gt;() {
             @Override
             public void call(Subscriber&lt;? super Boolean&gt; subscriber) {
                 try {
                     Log.d("DB: ", "saving Feed to DB");
                     for (FeedEntity feeds : feedEntity) {
                         feeds.save();
                     }
                     subscriber.onNext(true);
                     subscriber.onCompleted();
                 } catch (Exception exception) {
                     subscriber.onError(exception);
                 }
             }
         });
     } else return Observable.empty();
  }
  </code></pre>
  
  <p>in this last observable, i am not sure if i am doing it correctly. i.e. return true if database saving operation is done successfully. return false otherwise!</p>
  
  <p>also, should i return feedEntity is null?</p>
  
  <p>is that correct? and how should i check if observable returns true, false or empty Observable? </p>