title: How to handle "iterable must not be null" Flatmap Rxjava
body: <p>I am using FlatMap in my app for transform the items emitted by an Observable into  Iterables. I am getting "iterable must not be null".Because list is null.So I want to handle this situation.Can anyone tell me the solution.</p>
  
  <pre><code>flatMap(new Func1&lt;Chapters, Observable&lt;Page&gt;&gt;() {
                      @Override
                      public Observable&lt;Chapter&gt; call(Chapters chapterList) {
  
                          return Observable.from(chapterList);
                      }
                  })
  </code></pre>