title: sequence contains no elements in xamarin forms for listview
body: <p>I am trying to populate a ListView from a data. 
  In my XAML file I have written</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8" ?&gt;
  &lt;ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
               xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
               x:Class="FormDemos.Views.Feedback"&gt;
      &lt;ContentPage.Content&gt;
          &lt;Label&gt;I am Testimonials Page&lt;/Label&gt;
  
          &lt;ListView x:Name="FeedbackList" /&gt;
  
      &lt;/ContentPage.Content&gt;
  &lt;/ContentPage&gt;
  </code></pre>
  
  <p>In CS file</p>
  
  <pre><code>namespace FormDemos.Views
  {
      [XamlCompilation(XamlCompilationOptions.Compile)]
      public partial class Feedback : ContentPage
      {
          class City
          {
              public string Name
              {
                  get;
                  set;
              }
  
              public string State
              {
                  get;
                  set;
              }
          }
  
          public Feedback()
          {
              InitializeComponent();
              var cities = new List&lt;City&gt;() {
                  new City() {State = "FL", Name = "Miami"},
                  new City() {State = "CA", Name = "San Francisco"},
                  new City() {State = "CA", Name = "Los Angeles"},
                  new City() {State = "FL", Name = "Orlando"},
                  new City() {State = "TX", Name = "Houston"},
                  new City() {State = "NY", Name = "New York City"},
              };
              FeedbackList.ItemsSource = cities;
          }
      }
  }
  </code></pre>
  
  <p>Everytime I build this project I get Error "Sequence contains no elements". I have seen some online tutorials have the same code and running well. What's going wrong here?</p>