title: in flutter it shows me an error when i tryed to initialize a string...... it say it cant be null
body: <pre class="lang-dart prettyprint-override"><code>class Destination {
        String imageUrl;
        String city;
        String country;
        String description;
        List&lt;Activity&gt; activities;
  
        Destination({
          this.imageUrl,
          this.city,
          this.country,
          this.description,
          this.activities,
        });
  
  List&lt;Activity&gt; activities = [
    Activity(
      imageUrl: 'assets/images/stmarksbasilica.jpg',
      name: 'St. Mark\'s Basilica',
      type: 'Sightseeing Tour',
      startTimes: ['9:00 am', '11:00 am'],
      rating: 5,
      price: 30,
    ),
  </code></pre>