title: React default props are ignored
body: <p>I'm using <strong>Flow v.0.52</strong> typing in my <em>React</em> App, but I have a problem with correct assigning default props.</p>
  <h3>News.jsx</h3>
  <pre class="lang-js prettyprint-override"><code>class News extends Component {
    static defaultProps = {
      postList: {apiData: [], total: '0'},
    };
  
    componentDidMount() {
      this.props.getPostListData(this.props.lang, null, this.props.category);
    }
  
    props: {
      postList: {apiData: Array&lt;Content&gt;, total: string},
      getPostListData: Function,
    };
  
    render() {
      const { postList } = this.props;
      let renderNewsCards;
  
      if (postList.apiData.length !== 0) {
        renderNewsCards = (
          &lt;NewsCards ... /&gt;
        );
      } else {
        renderNewsCards = &lt;p style={{ textAlign: 'center' }}&gt;Loader...&lt;/p&gt;;
      }
  ...
  </code></pre>
  <p>In <strong>News.jsx</strong> component default props ignored and in result <code>postList.apiData.length</code> encounter type error <code>Uncaught TypeError: Cannot read property 'length' of undefined</code></p>
  <p><strong>P.S.</strong> <strong><em><a href="https://gist.github.com/Y-Taras/6cb04d51d7c0561f9396e562640d3bbf" rel="nofollow noreferrer">Link</a></em> to file  <code>News.jsx</code></strong></p>